**Parallel algorithmic techniques for combinatorial computation**.

D. Eppstein and Z. Galil.

*Ann. Rev. Comput. Sci.*3: 233–283, 1988.

Invited talk by Z. Galil,*16th Int. Coll. Automata, Languages and Programming,*Stresa, Italy, 1989.

Springer,*Lecture Notes in Comp. Sci.*372, 1989, pp. 304–318.This survey on parallel algorithms emphasized the use of basic subroutines such as prefix sums, Euler tours, ear decomposition, and matrix multiplication for solving more complicated graph problems.

**Planar orientations with low out-degree and compaction of adjacency matrices**.

M. Chrobak and D. Eppstein.

*Theor. Comp. Sci.*86 (2): 243–266, 1991.Describes efficient sequential and parallel algorithms for orienting the edges of an undirected planar graph so that each vertex has few outgoing edges. From such an orientation one can test in constant time whether a given edge exists. One consequence is a parallel algorithm to list all subgraphs isomorphic to \(K_3\) or \(K_4\). More recently this paper has been cited for its applications to scheduling update operations in parallel finite element methods.

**Equipartitions of graphs**.

D. Eppstein, J. Feigenbaum, and C.L. Li.

*Discrete Mathematics*91 (3): 239–248, 1991.Considers partitions of the vertices of a graph into equal subsets, with few pairs of subsets connected by edges. (Equivalently we view the graph as a subgraph of a product in which one factor is sparse.) A random graph construction shows that such a factorization does not always exist.

**Fast optimal parallel algorithms for maximal matching in sparse graphs**.

H. Asuri, M. Dillencourt, D. Eppstein, G. Lueker, and M. Molodowitch.

Tech. Rep. 92-01, ICS, UCI, 1992.We later discovered that the same results were published in a SPAA paper by Greg Shannon.

**Maintenance of a minimum spanning forest in a dynamic plane graph**.

D. Eppstein, G.F. Italiano, R. Tamassia, R.E. Tarjan, J. Westbrook, and M. Yung.

*1st ACM-SIAM Symp. Discrete Algorithms,*San Francisco, 1990, pp. 1–11.

*J. Algorithms*13 (1): 33–54, 1992 (special issue for 1st Symp. Discrete Algorithms).

Corrigendum,*J. Algorithms*15: 173, 1993.The complement of a minimum spanning tree is a maximum spanning tree in the dual graph. By applying this fact we can use a modified form of Sleator and Tarjan's dynamic tree data structure to update the MST in logarithmic time per update.

**Parallel recognition of series parallel graphs**.

D. Eppstein.

*Information & Computation*98: 41–55, 1992.Characterizes two-terminal series graphs in terms of a tree-like structure in their ear decompositions. Uses this characterization to construct parallel algorithms that recognize these graphs and construct their series-parallel decompositions.

**Finding the**.*k*smallest spanning trees

D. Eppstein.

*2nd Scand. Worksh. Algorithm Theory,*Bergen, Norway, 1990.

Springer,*Lecture Notes in Comp. Sci.*447, 1990, pp. 38–47.

*BIT*32: 237–248, 1992 (special issue for 2nd Scand. Worksh. Algorithm Theory).By removing edges not involved in some solution, and contracting edges involved in all solutions, we reduce the problem to one in a graph with O(

*k*) edges and vertices. This simplification step transforms any time bound involving*m*or*n*to one involving min(*m,**k*) or min(*n,**k*) respectively. This paper also introduces the geometric version of the*k*smallest spanning trees problem (the graph version was long known) which it solves using order (*k*+1) Voronoi diagrams.**Connectivity, graph minors, and subgraph multiplicity**.

D. Eppstein.

Tech. Rep. 92-06, ICS, UCI, 1992.

*J. Graph Th.*17: 409–416, 1993.It was known that planar graphs have O(

*n*) subgraphs isomorphic to K_{3}or K_{4}. That is, K_{3}and K_{4}have linear subgraph multiplicity. This paper shows that the graphs with linear subgraph multiplicity in the planar graphs are exactly the 3-connected planar graphs. Also, the graphs with linear subgraph multiplicity in the outerplanar graphs are exactly the 2-connected outerplanar graphs.More generally, let F be a minor-closed family, and let x be the smallest number such that some complete bipartite graph K

_{x,y}is a forbidden minor for F. Then the x-connected graphs have linear subgraph multiplicity for F, and there exists an (x − 1)-connected graph (namely K_{x − 1,x − 1}) that does not have linear subgraph multiplicity. When x ≤ 3 or when x = 4 and the minimal forbidden minors for F are triangle-free, then the graphs with linear subgraph multiplicity for F are exactly the x-connected graphs.Please refer only to the journal version, and not the earlier technical report: the technical report had a bug that was repaired in the journal version.

**Efficient sequential and parallel algorithms for computing recovery points in trees and paths**.

M. Chrobak, D. Eppstein, G.F. Italiano, and M. Yung.

*2nd ACM-SIAM Symp. Discrete Algorithms,*San Francisco, 1991, pp. 158–167.

ALCOM Report 91-74, University of Rome, 1991.Described slightly superlinear algorithms for partitioning a tree into a given number of subtrees, making them all as short as possible. Frederickson at the same conference further improved the sequential time to linear. There may still be something worth publishing in the parallel algorithms.

**Arboricity and bipartite subgraph listing algorithms**.

D. Eppstein.

Tech. Rep. 94-11, ICS, UCI, 1994.

*Inf. Proc. Lett.*51: 207–211, 1994.For any sparse family of graphs, one can list in linear time all complete bipartite subgraphs of a graph in the family. There are O(n) complete bipartite subgraphs of a graph in the family, and the sum of the numbers of vertices in these subgraphs is also O(n).

Nowadays these results can also be interpreted as a form of formal concept analysis. If a set of objects and attributes is sparse (e.g., if it is generated by adding objects and attributes one at a time, where each newly-added object is given O(1) attributes and each newly-added attribute is held by O(1) objects) then the total size of all concepts in its concept lattice is linear, and this lattice may be generated in linear time.

**Offline algorithms for dynamic minimum spanning tree problems**.

D. Eppstein.

*2nd Worksh. Algorithms and Data Structures,*Ottawa, Canada, 1991.

Springer,*Lecture Notes in Comp. Sci.*519, 1991, pp. 392–399.

Tech. Rep. 92-04, ICS, UCI, 1992.

*J. Algorithms*17: 237–250, 1994.Given a sequence of edge insertions and deletions in a graph, finds the corresponding sequence of minimum spanning tree changes, in logarithmic time per update. Similarly solves the planar geometric version of the problem (using a novel "mixed MST" formulation in which part of the input is a graph and part is a point set) in time O(log

^{2}*n*) for the Euclidean metric and O(log*n*log log*n*) for the rectilinear metric.**Sparsification—A technique for speeding up dynamic graph algorithms**.

D. Eppstein, Z. Galil, G.F. Italiano, and A. Nissenzweig.

*33rd IEEE Symp. Foundations of Comp. Sci.,*Pittsburgh, 1992, pp. 60–69.

Tech. Rep. RC 19272 (83907), IBM, 1993.

Tech. Rep. CS96-11, Univ. Ca' Foscari di Venezia, Oct. 1996.

*J. ACM*44 (5): 669–696, 1997.Uses a divide and conquer on the edge set of a graph, together with the idea of replacing subgraphs by sparser certificates, to make various dynamic algorithms as fast on dense graphs as they are on sparse graphs. Applications include random generation of spanning trees as well as finding the

*k*minimum weight spanning trees for a given parameter*k.***Improved sparsification**.

D. Eppstein, Z. Galil, and G.F. Italiano.

Tech. Rep. 93-20, ICS, UCI, 1993.Saves a log factor over dynamic graph algorithms in "Sparsification" and their applications, by dividing vertices instead of edges. Merged into the journal version of "Sparsification".

**Separator based sparsification for dynamic planar graph algorithms**.

D. Eppstein, Z. Galil, G.F. Italiano, and T. Spencer.

*25th ACM Symp. Theory of Computing,*San Diego, 1993, pp. 208–217.Replaces portions of a hierarchical separator decomposition with smaller certificates to achieve fast update times for various dynamic planar graph problems. Applications include finding the

*k*best spanning trees of a planar graph.**Separator based sparsification I: planarity testing and minimum spanning trees**.

D. Eppstein, Z. Galil, G.F. Italiano, and T. Spencer.

*J. Comp. Sys. Sci.*52: 3–27, 1996 (special issue for 25th STOC).First half of journal version of Separator based sparsification for dynamic planar graph algorithms.

**Separator based sparsification II: edge and vertex connectivity**.

D. Eppstein, Z. Galil, G.F. Italiano, and T. Spencer.

Tech. Rep. CS96-13, Univ. Ca' Foscari di Venezia, Oct. 1996.

*SIAM J. Computing*28 (1): 341–381, 1999.Second half of journal version of Separator based sparsification for dynamic planar graph algorithms.

**Worst-case bounds for subadditive geometric graphs**.

M. Bern and D. Eppstein.

*9th ACM Symp. Comp. Geom.,*San Diego, 1993, pp. 183–188.For many geometric graph problems for points in the unit square, such as minimum spanning trees, matching, and traveling salesmen, the sum of edge lengths is O(sqrt

*n*) and the sum of*d*th powers of edge lengths is O(log*n*). We provide a "gap theorem" showing that if these bounds do not hold for a class of graphs, both sums will instead be Omega(*n*). For traveling salesmen the O(log*n*) bound is tight but for some other graphs the sum of*d*th powers of edge lengths is O(1).**Clustering for faster network simplex pivots**.

D. Eppstein.

Tech. Rep. 93-19, ICS, UCI, 1993.

*5th ACM-SIAM Symp. Discrete Algorithms,*Arlington, 1994, pp. 160–166.

*Networks*35 (3): 173–180, 2000.Speeds up the worst case time per pivot for various versions of the network simplex algorithm for minimum cost flow problems. Uses techniques from dynamic graph algorithms as well as some simple geometric data structures.

**Finding the**.*k*shortest paths

D. Eppstein.

*35th IEEE Symp. Foundations of Comp. Sci.,*Santa Fe, 1994, pp. 154–165.

Tech. Rep. 94-26, ICS, UCI, 1994.

*SIAM J. Computing*28 (2): 652–673, 1998.This paper presents an algorithm that finds multiple short paths connecting two terminals in a graph (allowing repeated vertices and edges in the paths) in constant time per path after a preprocessing stage dominated by a single-source shortest path computation. The paths it finds are the

*k*shortest in the graph, where*k*is a parameter given as input to the algorithm.The

*k*shortest paths problem has many important applications for finding alternative solutions to geographic path planning problems, network routing, hypothesis generation in computational linguistics, and sequence alignment and metabolic pathway finding in bioinformatics. Although there have been many papers on the*k*shortest paths problem before and after this one, it has become frequently cited in those application areas. Additionally, it marks a boundary in the theoretical study of the problem: prior theoretical work largely concerned how quickly the problem could be solved, a line of research that was closed off by the optimal time bounds of this paper. Subsequent work has focused instead on devising efficient algorithms for more complex alternative formulations of the problem that avoid the repeated vertices and other shortcomings of the alternative paths produced by this formulation.The journal version also includes material from a separate 1995 technical report, "Finding common ancestors and disjoint paths in DAGs".

(Full paper – Graehl implementation – Jiménez-Marzal implementations – Shibuya implementation – Martins implementation – Cliff OpenStreetMap demo)

**Subgraph isomorphism in planar graphs and related problems**.

D. Eppstein.

Tech. Rep. 94-25, ICS, UCI, 1994.

*6th ACM-SIAM Symp. Discrete Algorithms,*San Francisco, 1995, pp. 632–640.

arXiv:cs.DS/9911003.

*J. Graph Algorithms and Applications*3 (3): 1–27, 1999.Uses an idea of Baker to cover a planar graph with subgraphs of low treewidth. As a consequence, any fixed pattern can be found as a subgraph in linear time; the same methods can be used to solve other planar graph problems including vertex connectivity, diameter, girth, induced subgraph isomorphism, and shortest paths. A companion paper, "Diameter and treewidth in minor-closed graph families", presents a result announced in the conference version of this paper, that exactly characterizes the minor-closed graph families for which the same techniques apply.

**Geometric lower bounds for parametric matroid optimization**.

D. Eppstein.

Tech. Rep. 95-11, ICS, UCI, 1995.

*27th ACM Symp. Theory of Computing,*Las Vegas, 1995, pp. 662–671.

*Disc. Comp. Geom.*20: 463–476, 1998.Considers graphs in which edge weights are linear functions of time. Shows nonlinear lower bounds on the number of different minimum spanning trees appearing over time by translation from geometric problem of lower envelopes of line segments. A matroid generalization has a better lower bound coming from many faces in line arrangements, and the uniform matroid problem is equivalent to the geometric

*k*-set problem.**3-Coloring in time O(1.3446**.^{n}): a no-MIS algorithm

R. Beigel and D. Eppstein.

Tech. Rep. 95-033, Electronic Coll. Computational Complexity, 1995.

*36th IEEE Symp. Foundations of Comp. Sci.*, 1995, pp. 444–453.

DIMACS Worksh. Faster Exact Solutions for NP-Hard Problems, 2000.Speeds up 3-coloring by solving a harder problem: constraint satisfaction in which each variable can take on one of three values and each constraint forbids a pair of variable assignments. The detailed solution involves several long hairy case analyses. Similar methods apply also to 3-list-coloring, 3-edge-coloring, and 3-SAT. The 3-SAT algorithm is fixed-parameter tractible in that it is polynomial time when the number of 3-variable clauses is O(log n). Merged into 3-coloring in time O(1.3289^n) for the journal version.

(DIMACS abstract and slides)

**Minimum range balanced cuts via dynamic subset sums**.

D. Eppstein.

Tech. Rep. 95-10, ICS, UCI, 1995.

*J. Algorithms*23: 375–385, 1997.Describes data structures for maintaining the solution of a dynamically changing subset sum problem, and uses them to find a cut in a graph minimizing the difference between the heaviest and lightest cut edge.

**Representing all minimum spanning trees with applications to counting and generation**.

D. Eppstein.

Tech. Rep. 95-50, ICS, UCI, 1995.Shows how to find for any edge weighted graph G an equivalent graph EG such that the minimum spanning trees of G correspond one-for-one with the spanning trees of EG. The equivalent graph can be constructed in time O(m+n log n) given a single minimum spanning tree of G. As a consequence one can find fast algorithms for counting, listing, and randomly generating MSTs. Also discusses similar equivalent graph constructions for shortest paths, minimum cost flows, and bipartite matching.

**Finding common ancestors and disjoint paths in DAGs**.

D. Eppstein.

Tech. Rep. 95-52, ICS, UCI, 1995.This paper describes algorithms for finding pairs of vertex-disjoint paths in a DAG, either connecting two given nodes to a common ancestor, or connecting two given pairs of terminals. The main results were merged into the journal version of "Finding the

*k*shortest paths".**Using sparsification for parametric minimum spanning tree problems**.

D. Fernández-Baca, G. Slutzki, and D. Eppstein.

*5th Scand. Worksh. Algorithm Theory,*Reykjavik, 1996.

Springer,*Lecture Notes in Comp. Sci.*1097, 1996, pp. 149–160.

*Nordic J. Computing*3 (4): 352–366, 1996 (special issue for 5th SWAT).Given a graph with edge weights that are linear functions of a parameter, finds the sequence of minimum spanning trees produced as the parameter varies, in total time O(mn log n), by combining ideas from "Sparsification" and "Geometric lower bounds". Also solves various problems of optimizing the parameter value, including one closely related to that in "Choosing subsets with maximum weighted average".

**Dynamic connectivity in digital images**.

D. Eppstein.

Tech. Rep. 96-13, ICS, UCI, 1996.

*Inf. Proc. Lett.*62: 121–126, 1997.Any algorithm that maintains the connected components of a bitmap image must take Omega(log

*n*/ log log*n*) time per change to the image. The problem can be solved in O(log*n*) time per change using dynamic planar graph techniques. We discuss applications to computer Go and other games.**On the parity of graph spanning tree numbers**.

D. Eppstein.

Tech. Rep. 96-14, ICS, UCI, 1996.Any bipartite Eulerian graph, any Eulerian graph with evenly many vertices, and any bipartite graph with evenly many vertices and edges, has an even number of spanning trees. More generally, a graph has evenly many spanning trees if and only if it has an Eulerian edge cut.

**Dynamic graph algorithms**.

D. Eppstein, Z. Galil, and G.F. Italiano.

Tech. Rep. CS96-11, Univ. Ca' Foscari di Venezia, Oct. 1996.

*Algorithms and Theoretical Computing Handbook,*M. J. Atallah, ed., CRC Press, 1999, chapter 8.

2nd. ed., CRC Press, 2010, Vol. I: General Concepts and Techniques, chapter 9, pp. 9–1 - 9-28.**Fast hierarchical clustering and other applications of dynamic closest pairs**.

D. Eppstein.

*9th ACM-SIAM Symp. Discrete Algorithms,*San Francisco, 1998, pp. 619–628.

arXiv:cs.DS/9912014.

*J. Experimental Algorithmics*5 (1): 1–23, 2000.This paper shows how to use my dynamic closest pair data structure from "Dynamic Euclidean minimum spanning trees" for some non-geometric problems including hierarchical clustering, greedy matching, and TSP heuristics. Experiments show variants of my data structures to be faster than previously used heuristics.

(Source code and experimental data – SODA paper – JEA home page)

**Geometric thickness of complete graphs**.

M. Dillencourt, D. Eppstein, and D. S. Hirschberg.

*6th Int. Symp. Graph Drawing,*Montreal, August 1998.

Springer,*Lecture Notes in Comp. Sci.*1547, 1998, pp. 102–110.

arXiv:math.CO/9910185.

*J. Graph Algorithms and Applications*4 (3): 5–17, 2000 (special issue for GD98).We define a notion of geometric thickness, intermediate between the previously studied concepts of graph thickness and book thickness: a graph has geometric thickness T if its vertices can be embedded in the plane, and its edges partitioned into T subsets, so that each subset forms a planar straight line graph. We then give upper and lower bounds on the geometric thickness of complete graphs.

**Diameter and treewidth in minor-closed graph families**.

D. Eppstein.

arXiv:math.CO/9907126.

*Algorithmica*27: 275–291, 2000 (special issue on treewidth, graph minors, and algorithms).This paper introduces the

*diameter-treewidth property*(later known as*bounded local treewidth*): a functional relationship between the diameter of its graph and its treewidth. Previously known results imply that planar graphs have bounded local treewidth; we characterize the other minor-closed families with this property. Specifically, minor-closed family F has bounded local treewidth if and only if there exists an*apex graph*G that is not in F; an apex graph is a graph that can be made planar by removing a single vertex. The minor-free families that exclude an apex graph (and therefore have bounded local treewidth) include the bounded-genus graphs (for which, as with planar graphs, we show a linear bound for the treewidth as a function of the diameter) and K_{3,a}-free graphs. As a consequence, subgraph isomorphism for subgraphs of bounded size and approximations to several NP-hard optimization problems can be computed efficiently on these graphs, extending previous results for planar graphs.Some of these results were announced in the conference version of "subgraph isomorphism for planar graphs and related problems" but not included in the journal version. Since its publication, there have been many more works on local treewidth. The class of problems that could be solved quickly on graphs of bounded local treewidth was extended and classified by Frick and Grohe, "Deciding first-order properties of locally tree-decomposable structures",

*J. ACM*48: 1184–1206, 2001; the proof that bounded local treewidth is equivalent to having an excluded apex minor was simplified, and the dependence of the treewidth on diameter improved, by a subsequent paper of Demaine and Hajiaghayi, "Diameter and treewidth in minor-closed graph families, revisited",*Algorithmica*40: 211–215, 2004. The concept of local treewidth is the basis for the theory of*bidimensionality*, a general framework for fixed-parameter-tractable algorithms and approximation algorithms in minor-closed graph families; for a survey, see Demaine and Hajiaghayi, "The bidimensionality theory and its algorithmic applications",*The Computer J.*51: 292–302, 2008.**Parametric and kinetic minimum spanning trees**.

P. K. Agarwal, D. Eppstein, L. J. Guibas, and M. R. Henzinger.

*39th IEEE Symp. Foundations of Comp. Sci.*, 1998, pp. 596–605..We describe algorithms for maintaining the minimum spanning tree in a graph in which the edge weights are piecewise linear functions of time that may change unpredictably. We solve the problem in time O(n

^{2/3}polylog n) per combinatorial change to the tree for general graphs, and in time O(n^{1/4}polylog n) per combinatorial change to the tree for planar graphs.**Algorithms for coloring quadtrees**.

M. Bern, D. Eppstein, and B. Hutchings.

arXiv:cs.CG/9907030.

*Algorithmica*32 (1): 87–94, 2002.We consider several variations of the problem of coloring the squares of a quadtree so that no two adjacent squares are colored alike. We give simple linear time algorithms for 3-coloring balanced quadtrees with edge adjacency, 4-coloring unbalanced quadtrees with edge adjacency, and 6-coloring balanced or unbalanced quadtrees with corner adjacency. The number of colors used by the first two algorithms is optimal; for the third algorithm, 5 colors may sometimes be needed.

**Guest editor's forward to special issue on dynamic graph algorithms**.

D. Eppstein.

*Algorithmica*22 (3): 233–234, 1998.**Setting parameters by example**.

D. Eppstein.

arXiv:cs.DS/9907001.

*40th IEEE Symp. Foundations of Comp. Sci.*, 1999, pp. 309–318.

*SIAM J. Computing*32 (3): 643–653, 2003.We introduce a class of "inverse parametric optimization" problems, in which one is given both a parametric optimization problem and a desired optimal solution; the task is to determine parameter values that lead to the given solution. We use low-dimensional linear programming and geometric sampling techniques to solve such problems for minimum spanning trees, shortest paths, and other optimal subgraph problems, and discuss applications in multicast routing, vehicle path planning, resource allocation, and board game programming.

**The distribution of cycle lengths in graphical models for iterative decoding**.

X. Ge, D. Eppstein, and P. Smyth.

arXiv:cs.DM/9907002.

Tech. Rep. 99-10, ICS, UCI, 1999.

IEEE Int. Symp. Information Theory, Sorrento, Italy, 2000.

*IEEE Trans. Information Theory*47 (6): 2549–2553, 2001.We compute the expected numbers of short cycles of each length in certain classes of random graphs used for turbocodes, estimate the probability that there are no such short cycles involving a given vertex, and experimentally verify our estimates. The scarcity of short cycles may help explain the empirically observed accuracy of belief-propagation based error-correction algorithms. Note, the TR, conference, and journal versions of this paper have slightly different titles.

**Graphs for dynamic geometry**.

D. Eppstein.

Invited talk, Worksh. Dynamic Graph Algorithms, Victoria, Canada, 2000.This talk surveys work on computational geometry algorithms that use dynamic graph data structures, and the different kinds of geometric graph arising in this work.

**3-coloring in time O(1.3289^n)**.

R. Beigel and D. Eppstein.

arXiv:cs.DS/0006046.

*J. Algorithms*54:2 (2005) 168-204.Journal paper combining 3-coloring algorithms from our FOCS '95 paper with improved bounds from our SODA '01 paper.

**Fast approximation of centrality**.

D. Eppstein and J. Wang.

arXiv:cs.DS/0009005.

*12th ACM-SIAM Symp. Discrete Algorithms,*Washington, 2001, pp. 228–229.

*J. Graph Algorithms & Applications*8 (1): 39–45, 2004.We use random sampling to quickly estimate, for each vertex in a graph, the average distance to all other vertices.

**Improved algorithms for 3-coloring, 3-edge-coloring, and constraint satisfaction**.

D. Eppstein.

arXiv:cs.DS/0009006.

*12th ACM-SIAM Symp. Discrete Algorithms,*Washington, 2001, pp. 329–337.Summarizes recent improvements to "3-Coloring in time O(1.3446

^{n}): a no-MIS algorithm". Merged with that paper for the journal version.(SODA talk slides – SODA paper)

**Small maximal independent sets and faster exact graph coloring**.

D. Eppstein.

arXiv:cs.DS/0011009.

*7th Worksh. Algorithms and Data Structures,*Providence, Rhode Island, 2001.

Springer,*Lecture Notes in Comp. Sci.*2125, 2001, pp. 462–470.

*J. Graph Algorithms and Applications*(special issue for WADS'01) 7 (2): 131–140, 2003.We show that any graph can be colored in time O(2.415

^{n}), by a dynamic programming procedure in which we extend partial colorings on subsets of the vertices by adding one more color for a maximal independent set. The time bound follows from limiting our attention to maximal independent subsets that are small relative to the previously colored subset, and from bounding the number of small maximal independent subsets that can occur in any graph.**Optimal Möbius transformations for information visualization and meshing**.

M. Bern and D. Eppstein.

arXiv:cs.CG/0101006.

*7th Worksh. Algorithms and Data Structures,*Providence, Rhode Island, 2001.

Springer,*Lecture Notes in Comp. Sci.*2125, 2001, pp. 14–25.We give linear-time quasiconvex programming algorithms for finding a Möbius transformation of a set of spheres in a unit ball or on the surface of a unit sphere that maximizes the minimum size of a transformed sphere. We can also use similar methods to maximize the minimum distance among a set of pairs of input points. We apply these results to vertex separation and symmetry display in spherical graph drawing, viewpoint selection in hyperbolic browsing, and element size control in conformal structured mesh generation.

**Separating geometric thickness from book thickness**.

D. Eppstein.

arXiv:math.CO/0109195.We show that geometric thickness and book thickness are not asymptotically equivalent: for every

*t*, there exists a graph with geometric thickness two and book thickness__>__*t*.**A steady state model for graph power laws**.

D. Eppstein and J. Wang.

2nd Int. Worksh. Web Dynamics, Honolulu, 2002.

arXiv:cs.DM/0204001.We propose a random graph model that (empirically) appears to have a power law degree distribution. Unlike previous models, our model is based on a Markov process rather than incremental growth. We compare our model with others in its ability to predict web graph clustering behavior.

**Separating thickness from geometric thickness**.

D. Eppstein.

arXiv:math.CO/0204252.

10th Int. Symp. Graph Drawing, Irvine, 2002.

Springer,*Lecture Notes in Comp. Sci.*2528, 2002, pp. 150–161.

In*Towards a Theory of Geometric Graphs*, AMS, 2004, Contemporary Math 342, J. Pach, ed., pp. 75–86.We show that thickness and geometric thickness are not asymptotically equivalent: for every

*t*, there exists a graph with thickness three and geometric thickness__>__*t*. The proof uses Ramsey-theoretic arguments similar to those in "Separating book thickness from thickness".**Algorithms for media**.

D. Eppstein and J.-C. Falmagne.

arXiv:cs.DS/0206033.

Int. Conf. Ordinal and Symbolic Data Analysis, Irvine, 2003.

*Discrete Applied Mathematics*156 (8): 1308–1320, 2008.Falmagne recently introduced the concept of a medium, a combinatorial object encompassing hyperplane arrangements, topological orderings, acyclic orientations, and many other familiar structures. We find efficient solutions for several algorithmic problems on media: finding short reset sequences, shortest paths, testing whether a medium has a closed orientation, and listing the states of a medium given a black-box description.

**Dynamic generators of topologically embedded graphs**.

D. Eppstein.

arXiv:cs.DS/0207082.

*14th ACM-SIAM Symp. Discrete Algorithms,*Baltimore, 2003, pp. 599–608.We describe a decomposition of graphs embedded on 2-dimensional manifolds into three subgraphs: a spanning tree, a dual spanning tree, and a set of leftover edges with cardinality determined by the genus of the manifold. This tree-cotree decomposition allows us to find efficient data structures for dynamic graphs (allowing updates that change the surface), better constants in bounded-genus graph separators, and efficient algorithms for tree-decomposition of bounded-genus bounded-diameter graphs.

**Confluent drawings: visualizing non-planar diagrams in a planar way**.

M. Dickerson, D. Eppstein, M. T. Goodrich, and J. Meng.

arXiv:cs.CG/0212046.

11th Int. Symp. Graph Drawing, Perugia, Italy, 2003.

Springer,*Lecture Notes in Comp. Sci.*2912, 2004, pp. 1–12.

*J. Graph Algorithms and Applications*(special issue for GD'03) 9 (1): 31–52, 2005.We describe a new method of drawing graphs, based on allowing the edges to be merged together and drawn as "tracks" (similar to train tracks). We present heuristics for finding such drawings based on my previous algorithms for finding maximal bipartite subgraphs, prove that several important families of graphs have confluent drawings, and provide examples of other graphs that can not be drawn in this way.

**The traveling salesman problem for cubic graphs**.

D. Eppstein.

arXiv:cs.DS/0302030.

*8th Worksh. Algorithms and Data Structures,*Ottawa, 2003.

Springer,*Lecture Notes in Comp. Sci.*2748, 2003, pp. 307–318.*J. Graph Algorithms and Applications*11 (1): 61–81, 2007.We find improved exponential-time algorithms for exact solution of the traveling salesman problem on graphs of maximum degree three and four. We also consider related problems including counting the number of Hamiltonian cycles in such graphs.

**Testing bipartiteness of geometric intersection graphs**.

D. Eppstein.

arXiv:cs.CG/0307023.

*15th ACM-SIAM Symp. Discrete Algorithms,*New Orleans, 2004, pp. 853–861.

*ACM Trans. Algorithms*5(2):15, 2009.We consider problems of partitioning sets of geometric objects into two subsets, such that no two objects within the same subset intersect each other. Typically, such problems can be solved in quadratic time by constructing the intersection graph and then applying a graph bipartiteness testing algorithm; we achieve subquadratic times for general objects, and O(n log n) times for balls in R^d or simple polygons in the plane, by using geometric data structures, separator based divide and conquer, and plane sweep techniques, respectively. We also contrast the complexity of bipartiteness testing with that of connectivity testing, and provide evidence that for some classes of object, connectivity is strictly harder due to a computational equivalence with Euclidean minimum spanning trees.

**The geometric thickness of low degree graphs.**

C. Duncan, D. Eppstein, and S. Kobourov.

arXiv:cs.CG/0312056.

*20th ACM Symp. Comp. Geom.,*Brooklyn, 2004, pp. 340–346.We show that graphs with maximum degree four have geometric thickness at most two, by partitioning them into degree two subgraphs and applying simultaneous embedding techniques.

**Single-strip triangulation of manifolds with arbitrary topology.**

D. Eppstein and M. Gopi.

13th Video Review of Computational Geometry, 2004.

*20th ACM Symp. Comp. Geom.,*Brooklyn, 2004, pp. 455–456 (abstract for video).

*25th Conf. Eur. Assoc. for Computer Graphics (EuroGraphics '04)*, Grenoble, 2004 (2nd best paper award).

*Eurographics Forum*23 (3): 371–379, 2004.

arXiv:cs.CG/0405036.We describe a new algorithm, based on graph matching, for subdividing a triangle mesh (without boundary) so that it has a Hamiltonian cycle of triangles, and prove that this subdivision process increases the total number of triangles in the mesh by at most a factor of 3/2. We also prove lower bounds on the increase needed for meshes with and without boundary.

**The effect of faults on network expansion.**

A. Bagchi, A. Bhargava, A. Chaudhary, D. Eppstein, and C. Scheideler.

arXiv:cs.DC/0404029.

*16th ACM Symp. Parallelism in Algorithms and Architectures*, Barcelona, 2004, pp. 286–293.

*Theory of Computing Systems*39 (6): 903–928, 2006.Studies the resilience of distributed computation networks against adversarial and random fault models; shows that, in both models, certain networks can withstand constant fault probabilities and still contain a large subnetwork with similar expansion to the original.

**The lattice dimension of a graph.**

D. Eppstein.

arXiv:cs.DS/0402028.

*Eur. J. Combinatorics*26 (6): 585–592, 2005.Describes a polynomial time algorithm for isometrically embedding graphs into an integer lattice of the smallest possible dimension. The technique involves maximum matching in an auxiliary graph derived from a partial cube representation of the input.

**Algorithms for drawing media.**

D. Eppstein.

arXiv:cs.DS/0406020.

12th Int. Symp. Graph Drawing, New York, 2004.

Springer,*Lecture Notes in Comp. Sci.*3383, 2004, pp. 173–183.We describe two algorithms for finding planar layouts of partial cubes: one based on finding the minimum-dimension lattice embedding of the graph and then projecting the lattice onto the plane, and the other based on representing the graph as the planar dual to a weak pseudoline arrangement.

Due to editorial mishandling there will be no journal version of this paper: I submitted it to a journal in 2004, the reviews were supposedly sent back to me in 2005, but I didn't receive them and didn't respond to them, leading the editors to assume that I intended to withdraw the submission. Large portions of the paper have since been incorporated into my book

*Media Theory*, making journal publication moot.**Confluent layered drawings**.

D. Eppstein, M. T. Goodrich, and J. Meng.

12th Int. Symp. Graph Drawing, New York, 2004.

Springer,*Lecture Notes in Comp. Sci.*3383, 2004, pp. 184–194.

arXiv:cs.CG/0507051.

*Algorithmica*47 (4): 439–452 (special issue for Graph Drawing), 2007.Describes a graph drawing technique combining ideas of confluent drawing with Sugiyama-style layered drawing. Uses a reduction to graph coloring to find and visualize sets of bicliques in each layer.

**All maximal independent sets and dynamic dominance for sparse graphs.**

D. Eppstein.

arXiv:cs.DS/0407036.

*16th ACM-SIAM Symp. Discrete Algorithms,*Vancouver, 2005, pp. 451–459.

*ACM Trans. Algorithms*5(4):A38, 2009.We show how to apply reverse search to list all maximal independent sets in bounded-degree graphs in constant time per set, in graphs from minor closed families in linear time per set, and in sparse graphs in subquadratic time per set. The latter two results rely on new data structures for maintaining a dynamic vertex set in a graph and quickly testing whether the set dominates all other vertices.

**The weighted maximum-mean subtree and other bicriterion subtree problems.**

J. Carlson and D. Eppstein.

arXiv:cs.CG/0503023.

*Proc. 10th Scand. Worksh. Algorithm Theory (SWAT 2006)*.

Springer,*Lecture Notes in Comp. Sci.*4059, 2006, pp. 397–408.We give a linear time algorithm for pruning a node-weighted tree to maximize the average node weight of the pruned subtree; this problem was previously studied under the less obvious name "The Fractional Prize-Collecting Steiner Tree Problem on Trees".

**Delta-confluent drawings**.

D. Eppstein, M. T. Goodrich, and J. Meng.

13th Int. Symp. Graph Drawing, Limerick, Ireland, 2005.

Springer,*Lecture Notes in Comp. Sci.*3843, 2006, pp. 165–176.

arXiv:cs.CG/0510024.

We characterize the graphs that can be drawn confluently with a single confluent track that is tree-like except for three-way Delta junctions, as being exactly the distance hereditary graphs. Based on this characterization, we develop efficient algorithms for drawing these graphs.

**Nonrepetitive paths and cycles in graphs with application to Sudoku**.

D. Eppstein.

arXiv:cs.DS/0507053.We describe algorithms and hardness results for finding paths in edge-labeled graphs such that no two consecutive edges have the same label, and use our algorithms to implement heuristics for a program that automatically solves and generates Sudoku puzzles.

**Drawings of planar graphs with few slopes and segments.**

V. Dujmović, D. Eppstein, M. Suderman, and D. R. Wood.

arXiv:math.CO/0606450.

*Comp. Geom. Theory & Applications*38: 194–212, 2007.We study straight-line drawings of planar graphs with few segments and few slopes. Optimal results are obtained for all trees. Tight bounds are obtained for outerplanar graphs, 2-trees, and planar 3-trees. We prove that every 3-connected plane graph on n vertices has a plane drawing with at most 5n/2 segments and at most 2n slopes. We prove that every cubic 3-connected plane graph has a plane drawing with three slopes (and three bends on the outerface).

**Cubic partial cubes from simplicial arrangements.**

D. Eppstein.

arXiv:math.CO/0510263.

*Electronic J. Combinatorics*13(1), Paper R79, 2006.We show how to construct a cubic partial cube from any simplicial arrangement of lines or pseudolines in the projective plane. As a consequence, we find nine new infinite families of cubic partial cubes as well as many sporadic examples.

**Single triangle strip and loop on manifolds with boundaries.**

A. Bushan, P. Diaz-Gutierrez, D. Eppstein, and M. Gopi.

Tech. Rep. 05-11, UC Irvine, School of Information and Computer Science, 2005.

Proc. 19th Brazilian Symp. Computer Graphics and Image Processing (SIBGRAPI 2006), pp. 221–228.This follows on to our previous paper on using graph matching to cover a triangulated polyhedral model with a single triangle strip by extending the algorithms to models with boundaries. We provide two methods: one is based on using an algorithm for the Chinese Postman problem to find a small set of triangles to split in order to find a perfect matching in the dual mesh, while the other augments the model with virtual triangles to remove the boundaries and merges the strips formed by our previous algorithm on this augmented model. We implement the algorithms and report some preliminary experimental results.

**Interconnect criticality driven delay relaxation.**

L. Singhal, E. Bozorgzadeh, and D. Eppstein.

*IEEE Trans. CAD*26 (10): 1803–1817, 2007.We consider a problem of assigning delays to components in a circuit so that each component is part of a critical path, but the number of edges belonging to critical paths is minimized. We show the problem to be NP-complete via a reduction from finding independent dominating sets in bipartite graphs minimizing dominated edges, and give experimental results on heuristics.

**Upright-quad drawing of \(st\)-planar learning spaces.**

D. Eppstein.

arXiv:cs.CG/0607094.

14th Int. Symp. Graph Drawing, Karlsruhe, Germany, 2006.

Springer,*Lecture Notes in Comp. Sci.*4372, 2007, pp. 282–293.

*J. Graph Algorithms and Applications*12 (1): 51–72, 2008 (special issue for GD'06).We consider graph drawing algorithms for learning spaces, a type of \(st\)-oriented partial cube derived from antimatroids and used to model states of knowledge of students. We show how to draw any \(st\)-planar learning space so all internal faces are convex quadrilaterals with the bottom side horizontal and the left side vertical, with one minimal and one maximal vertex. Conversely, every such drawing represents an \(st\)-planar learning space. We also describe connections between these graphs and arrangements of translates of a quadrant.

**Trees with convex faces and optimal angles.**

J. Carlson and D. Eppstein.

arXiv:cs.CG/0607113.

14th Int. Symp. Graph Drawing, Karlsruhe, Germany, 2006.

Springer,*Lecture Notes in Comp. Sci.*4372, 2007, pp. 77–88.We consider drawings of trees which, if the leaf edges were extended to infinite rays, would form partitions of the plane into unbounded convex polygons. For such a drawing the edges may be chosen independently without any possibility of edge crossing. We show how to choose the angles of such drawings to optimize the angular resolution of the drawing.

**Choosing colors for geometric graphs via color space embeddings.**

M. Dillencourt, D. Eppstein, and M. T. Goodrich.

arXiv:cs.CG/0609033.

14th Int. Symp. Graph Drawing, Karlsruhe, Germany, 2006.

Springer,*Lecture Notes in Comp. Sci.*4372, 2007, pp. 294–305.We show how to choose colors for the vertices of a graph drawing in such a way that all colors are easily distinguishable, but such that adjacent vertices have especially dissimilar colors, by considering the problem as one of embedding the graph into a three-dimensional color space.

**Happy endings for flip graphs.**

D. Eppstein.

arXiv:cs.CG/0610092.

*23rd ACM Symp. Comp. Geom.,*Gyeongju, South Korea, 2007, pp. 92–101.

*J. Computational Geometry*1 (1): 3–28, 2010.We show that the triangulations of a finite point set form a flip graph that can be embedded isometrically into a hypercube, if and only if the point set has no empty convex pentagon. Point sets of this type include convex subsets of lattices, points on two lines, and several other infinite families. As a consequence, flip distance in such point sets can be computed efficiently.

**Manhattan orbifolds.**

D. Eppstein.

arXiv:math.MG/0612109.

*Topology and its Applications*157 (2): 494–507, 2009.We investigate a class of metrics for 2-manifolds in which, except for a discrete set of singular points, the metric is locally isometric to an L

_{1}metric, and show that with certain additional conditions such metrics are injective. We use this construction to find the tight span of squaregraphs and related graphs, and we find an injective metric that approximates the distances in the hyperbolic plane analogously to the way the rectilinear metrics approximate the Euclidean distance.**Edges and switches, tunnels and bridges.**

D. Eppstein, M. van Kreveld, E. Mumford, and B. Speckmann.

23rd European Workshop on Computational Geometry (EWCG'07), Graz, 2007.

*10th Worksh. Algorithms and Data Structures,*Halifax, Nova Scotia, 2007.

*Springer, Lecture Notes in Comp. Sci.*4619, 2007, pp. 77–88.

Tech. Rep. UU-CS-2007-042, Utrecht Univ., Dept. of Information and Computing Sciences, 2007.

arXiv:0705.0413.

*Comp. Geom. Theory & Applications*42 (8): 790–802, 2009 (special issue for EWCG'07).We show how to solve several versions of the problem of casing graph drawings: that is, given a drawing, choosing to draw one edge as upper and one lower at each crossing in order to improve the drawing's readability.

**On verifying and engineering the well-gradedness of a union-closed family**.

D. Eppstein, J.-C. Falmagne, and H. Uzun.

arXiv:0704.2919.

38th Meeting of the European Mathematical Psychology Group, Luxembourg, 2007.

*J. Mathematical Psychology*53 (1): 34–39, 2009.We describe tests for whether the union-closure of a set family is well-graded, and algorithms for finding a minimal well-graded union-closed superfamily of a given set family.

**Recognizing partial cubes in quadratic time**.

D. Eppstein.

arXiv:0705.1025.

*19th ACM-SIAM Symp. Discrete Algorithms,*San Francisco, 2008, pp. 1258–1266.

*J. Graph Algorithms and Applications*15 (2): 269–293, 2011.We show how to test whether a graph is a partial cube, and if so embed it isometrically into a hypercube, in time O(n

^{2}), improving previous O(nm)-time solutions; here n is the number of vertices and m is the number of edges. The ideas are to use bit-parallelism to speed up previous approaches to the embedding step, and to verify that the resulting embedding is isometric using an all-pairs shortest path algorithm from "algorithms for media".(slides)

**Geometry of partial cubes**.

D. Eppstein.

Invited talk at 6th Slovenian International Conference on Graph Theory, Bled, Slovenia, 2007.I survey some of my recent results on geometry of partial cubes, including lattice dimension, graph drawing, cubic partial cubes, and partial cube flip graphs of triangulations.

(Slides)

**The Complexity of Bendless Three-Dimensional Orthogonal Graph Drawing**.

D. Eppstein.

arXiv:0709.4087.

*Proc. 16th Int. Symp. Graph Drawing*, Heraklion, Crete, 2008.

Springer,*Lecture Notes in Comp. Sci.*5417, 2009, pp. 78–89.

*J. Graph Algorithms and Applications*17 (1): 35–55, 2013.Defines a class of orthogonal graph drawings formed by a point set in three dimensions for which axis-parallel line contains zero or two vertices, with edges connecting pairs of points on each nonempty axis-parallel line. Shows that the existence of such a drawing can be defined topologically, in terms of certain two-dimensional surface embeddings of the same graph. Based on this equivalence, describes algorithms, graph-theoretic properties, and hardness results for graphs of this type.

(Slides from talk at U. Arizona, February 2008 – Slides from GD08) )

**Media Theory: Interdisciplinary Applied Mathematics**.

D. Eppstein, J.-C. Falmagne, and S. Ovchinnikov.

Springer, 2007, ISBN 978-3-540-71696-9.Many combinatorial structures such as the set of acyclic orientations of a graph, weak orderings of a set of elements, or chambers of a hyperplane arrangement have the structure of a partial cube, a graph in which vertices may be labeled by bitvectors in such a way that graph distance equals Hamming distance. This book analyzes these structures in terms of operations that change one vertex to another by flipping a single bit of the bitvector labelings. It incorporates material from several of my papers including "Algorithms for Media", "Algorithms for Drawing Media", "Upright-Quad Drawing of st-Planar Learning Spaces", and "The Lattice Dimension of a Graph".

(Publisher's web site – Reinhard Suck's review in J. Math. Psych. – Reinhard Suck's review in MathSciNet)

**Learning sequences**.

D. Eppstein.

arXiv:0803.4030.

How to implement an antimatroid, with applications in computerized education.

**Principles of Graph Drawing**.

D. Eppstein.

Talk at Inst. for Mathematical Behavioral Sciences, May 2008.

Talk at Technical University of Eindhoven, September 2008.**Approximate Topological Matching of Quadrilateral Meshes**.

D. Eppstein, M. T. Goodrich, E. Kim, and R. Tamstorf.

*Proc. IEEE Int. Conf. Shape Modeling and Applications (SMI 2008)*, Stony Brook, New York, pp. 83–92.

*The Visual Computer*25 (8): 771–783, 2009.We formalize problems of finding large approximately-matching regions of two related but not completely isomorphic quadrilateral meshes, show that these problems are NP-complete, and describe a natural greedy heuristic that is guaranteed to find good matches when the mismatching parts of the meshes are small.

(Preprint)

**Succinct greedy geometric routing using hyperbolic geometry**.

D. Eppstein and M. T. Goodrich.

arXiv:0806.0341.

*Proc. 16th Int. Symp. Graph Drawing*, Heraklion, Crete, 2008

(under the different title "Succinct greedy graph drawing in the hyperbolic plane"),

Springer,*Lecture Notes in Comp. Sci.*5417, 2009, pp. 14–25.

*IEEE Transactions on Computing*60 (11): 1571–1580, 2011.Greedy drawing is an idea for encoding network routing tables into the geometric coordinates of an embedding of the network, but most previous work in this area has ignored the space complexity of these encoded tables. We refine a method of R. Kleinberg for embedding arbitrary graphs into the hyperbolic plane, which uses linearly many bits to represent each vertex, and show that only logarithmic bits per point are needed.

**Isometric diamond subgraphs**.

D. Eppstein.

arXiv:0807.2218.

*Proc. 16th Int. Symp. Graph Drawing*, Heraklion, Crete, 2008.

Springer,*Lecture Notes in Comp. Sci.*5417, 2009, pp. 384–389.

We describe polynomial time algorithms for determining whether an undirected graph may be embedded in a distance-preserving way into the hexagonal tiling of the plane, the diamond structure in three dimensions, or analogous structures in higher dimensions. The graphs that may be embedded in this way form an interesting subclass of the partial cubes.

(Slides)

**Studying (non-planar) road networks through an algorithmic lens**.

D. Eppstein, and M. T. Goodrich.

arXiv:0808.3694.

*Proc. 16th ACM SIGSPATIAL Int. Conf. Advances in Geographic Information Systems (ACM GIS 2008)*, Article 16 (best paper award).

Invited talk at INFORMS 2009, San Diego.We examine US road network data and show that, contrary to the assumptions of much past GIS work, these networks are highly nonplanar. We introduce a class of "multiscale dispersed" networks that better fit the data; these networks are defined by a family of disks of varying sizes such that, if a small number of outliers is removed, the remaining disks cover each point of the plane a constant number of times. As we show, these networks have good graph separators, allowing for efficient algorithms for minimum spanning trees, graph Voronoi diagrams, and related problems.

**Linear-time algorithms for geometric graphs with sublinearly many crossings**.

D. Eppstein, M. T. Goodrich, and D. Strash.

arXiv:0812.0893.

*20th ACM-SIAM Symp. Discrete Algorithms,*New York, 2009, pp. 150–159.

*SIAM J. Computing*39 (8): 3814–3829, 2010.If a connected graph corresponds to a set of points and line segments in the plane, in such a way that the number of crossing pairs of line segments is sublinear in the size of the graph by an iterated-log factor, then we can find the arrangement of the segments in linear time. It was previously known how to find the arrangement in linear time when the number of crossings is superlinear by an iterated-log factor, so the only remaining open case is when the number of crossings is close to the size of the graph.

**Finding large clique minors is hard**.

D. Eppstein.

arXiv:0807.0007.

*J. Graph Algorithms and Applications*13 (2): 197–204, 2009.Proves that it's NP-complete to compute the Hadwiger number of a graph.

**Area-universal rectangular layouts**.

D. Eppstein, E. Mumford, B. Speckmann, and K. Verbeek.

arXiv:0901.3924.

*25th Eur. Worksh. Comp. Geom.*, Brussels, Belgium, 2009.

*25th ACM Symp. Comp. Geom.,*Aarhus, Denmark, 2009, pp. 267–276.A partition of a rectangle into smaller rectangles is "area-universal" if any vector of areas for the smaller rectangles can be realized by a combinatorially equivalent partition. These partitions may be applied, for instance, to cartograms, stylized maps in which the shapes of countries have been distorted so that their areas represent numeric data about the countries. We characterize area-universal layouts, describe algorithms for finding them, and discuss related problems. The algorithms for constructing area-universal layouts are based on the distributive lattice structure of the set of all layouts of a given dual graph.

Merged with "Orientation-constrained rectangular layouts" to form the journal version, "Area-universal and constrained rectangular layouts".

**The Fibonacci dimension of a graph**.

S. Cabello, D. Eppstein, and S. Klavžar.

IMFM Preprint 1084, Institute of Mathematics, Physics and Mechanics, Univ. of of Ljubljana, 2009.

arXiv:0903.2507.

*Electronic J. Combinatorics*18(1), Paper P55, 2011.We investigate isometric embeddings of other graphs into Fibonacci cubes, graphs formed from the families of fixed-length bitstrings with no two consecutive ones.

**The h-index of a graph and its application to dynamic subgraph statistics**.

D. Eppstein and E. S. Spiro.

arXiv:0904.3741.

Algorithms and Data Structures Symposium (WADS), Banff, Canada.

Springer,*Lecture Notes in Comp. Sci.*5664, 2009, pp. 278–289.

*J. Graph Algorithms and Applications*16 (2): 543–567, 2012.We define the h-index of a graph to be the maximum h such that the graph has h vertices each of which has degree at least h. We show that the h-index, and a partition of the graph into high and low degree vertices, may be maintained in constant time per update. Based on this technique, we show how to maintain the number of triangles in a dynamic graph in time O(h) per update; this problem is motivated by Markov Chain Monte Caro simulation of the Exponential Random Graph Model used for simulation of social networks. We also prove bounds on the h-index for scale-free graphs and investigate the behavior of the h-index on a corpus of real social networks.

(Slides)

**Orientation-constrained rectangular layouts**.

D. Eppstein and E. Mumford.

arXiv:0904.4312.

Algorithms and Data Structures Symposium (WADS), Banff, Canada.

Springer,*Lecture Notes in Comp. Sci.*5664, 2009, pp. 266–277.We show how to find a stylized map in which regions have been replaced by rectangles, preserving adjacencies between regions, with constraints on the orientations of adjacencies between regions. For an arbitrary dual graph representing a set of adjacencies, and an arbitrary set of orientation constraints, we can determine whether there exists a rectangular map satisfying those constraints in polynomial time. The algorithm is based on a representation of the set of all layouts for a given dual graph as a distributive lattice, and on Birkhoff's representation theorem for distributive lattices.

Merged with "Area-universal rectangular layouts" to form the journal version, "Area-universal and constrained rectangular layouts".

(Slides)

**Combinatorics and geometry of finite and infinite squaregraphs**.

H.-J. Bandelt, V. Chepoi, and D. Eppstein.

arXiv:0905.4537.

*SIAM J. Discrete Math.*24 (4): 1399–1440, 2010.Characterizes squaregraphs as duals of triangle-free hyperbolic line arrangements, provides a forbidden subgraph characterization of them, describes an algorithm for finding minimum subsets of vertices that generate the whole graph by medians, and shows that they may be isometrically embedded into Cartesian products of five (but not, in general, fewer than five) trees.

**Graph-theoretic solutions to computational geometry problems**.

D. Eppstein.

Invited talk at the 35th International Workshop on Graph-Theoretic Concepts in Computer Science (WG 2009), Montpellier, France, 2009.

Springer,*Lecture Notes in Comp. Sci.*5911, 2009, pp. 1–16.

arXiv:0908.3916.We survey problems in computational geometry that may be solved by constructing an auxiliary graph from the problem and solving a graph-theoretic problem on the auxiliary graph. The problems considered include the art gallery problem, partitioning into rectangles, minimum diameter clustering, bend minimization in cartogram construction, mesh stripification, optimal angular resolution, and metric embedding.

**Optimal angular resolution for face-symmetric drawings**.

D. Eppstein and K. Wortman.

arXiv:0907.5474.

*J. Graph Algorithms and Applications*15 (4): 551–564, 2011.We consider drawings of planar partial cubes in which all interior faces are centrally symmetric convex polygons, as in my previous paper Algorithms for Drawing Media. Among all drawings of this type, we show how to find the one with optimal angular resolution. The solution involves a transformation from the problem into the parametric negative cycle detection problem: given a graph in which the edge weights are linear functions of a parameter λ, find the minimum value of λ for which the graph contains no negative cycles.

**Going off-road: transversal complexity in road networks**.

D. Eppstein, M. T. Goodrich, and L. Trott.

arXiv:0909.2891.

Proc. 17th ACM SIGSPATIAL Int. Conf. Advances in Geographic Information Systems, Seattle, 2009, pp. 23–32.Shows both theoretically and experimentally that the number of times a random line crosses a road network is asymptotically upper bounded by the square root of the number of road segments.

**Paired approximation problems and incompatible inapproximabilities**.

D. Eppstein.

arXiv:0909.1870.

*21st ACM-SIAM Symp. Discrete Algorithms*, Austin, Texas, 2010, pp. 1076–1086.Considers situations in which two hard approximation problems are presented by means of a single input. In many cases it is possible to guarantee that one or the other problem can be approximated to within a better approximation ratio than is possible for approximating it as a single problem. For instance, it is possible to find either a (1+ε)-approximation to a 1-2 TSP defined from a graph or a n

^{ε}-approximation to the maximum independent set of the same graph, despite lower bounds showing nonexistence of approximation schemes for 1-2 TSP and nonexistence of approximations better than n^{1 − ε}for independent set. However, for some other pairs of problems, such as hitting set and set cover, we show that solving the paired problem approximately is no easier than solving either problem independently.(Slides)

**Steinitz theorems for orthogonal polyhedra**.

D. Eppstein and E. Mumford.

arXiv:0912.0537.

*26th Eur. Worksh. Comp. Geom.*, Dortmund, Germany, 2010.

*26th ACM Symp. Comp. Geom.,*Snowbird, Utah, 2010, pp. 429–438.

*J. Computational Geometry*5 (1): 179–244, 2014.We provide a graph-theoretic characterization of three classes of nonconvex polyhedra with axis-parallel sides, analogous to Steinitz's theorem characterizing the graphs of convex polyhedra.

The journal version has the slightly different title "Steinitz theorems for simple orthogonal polyhedra".

(Slides)

**Ramified rectilinear polygons: coordinatization by dendrons**.

H.-J. Bandelt, V. Chepoi, and D. Eppstein.

arXiv:1005.1721.

*Disc. Comp. Geom.*54 (4): 771–797, 2015.

We characterize the graphs that can be isometrically embedded into the Cartesian product of two trees (partial double dendrons), and the metric spaces obtained as the median complexes of these graphs. These spaces include the space of geodesic distance in axis-parallel polygons in the L

_{1}plane, hence the title. An algorithm based on lexicographic breadth-first search can be used to recognize partial double dendrons in linear time.**Regular labelings and geometric structures**.

D. Eppstein.

arXiv:1007.0221.

Invited to 22nd Canadian Conference on Computational Geometry (CCCG 2010).

Invited to*Proc. 21st International Symposium on Algorithms and Computation (ISAAC 2010)*, Jeju, Korea, 2010.

Springer,*Lecture Notes in Comp. Sci.*6506, 2010, p. 1.

We survey regular labelings for straight-line embedding of planar graphs on grids, rectangular partitions, and orthogonal polyhedra, and the many similarities between these different types of labeling.

**Flows in one-crossing-minor-free graphs**.

E. Chambers and D. Eppstein.

arXiv:1007.1484.

*Proc. 21st International Symposium on Algorithms and Computation (ISAAC 2010)*, Jeju, Korea, 2010.

Springer,*Lecture Notes in Comp. Sci.*6506, 2010, pp. 241–252.

*J. Graph Algorithms and Applications*17 (3): 201–220, 2013.We show that the maximum flow problem can be solved in near-linear time for K

_{5}-minor-free and K_{3,3}-minor-free graphs. The same result also holds for H-minor-free graphs when H can be embedded in the plane with one crossing and a structural decomposition of the input flow graph is given.**Listing all maximal cliques in sparse graphs in near-optimal time**.

D. Eppstein, M. Löffler, and D. Strash.

arXiv:1006.5440.

Workshop on Exact Algorithms for NP-Hard Problems, Dagstuhl, Germany, 2010.

*Proc. 21st International Symposium on Algorithms and Computation (ISAAC 2010)*, Jeju, Korea, 2010.

Springer,*Lecture Notes in Comp. Sci.*6506, 2010, pp. 403–414.

We describe an algorithm for finding all maximal cliques in a graph, in time O(dn3

^{d/3}) where n is the number of vertices and d is the degeneracy of the graph, a standard measure of its sparsity. This time bound matches the worst-case output size for these parameters. The algorithm modifies the Bron-Kerbosch algorithm for maximal cliques by ordering the vertices by degree in the outer recursive call of the algorithm.For the journal version, see "Listing all maximal cliques in large sparse real-world graphs," which combines results from this and a different conference paper.

**Drawing graphs in the plane with a prescribed outer face and polynomial area**.

E. Chambers, D. Eppstein, M. T. Goodrich, and M. Löffler.

*Proc. 18th Int. Symp. Graph Drawing*, Konstanz, Germany, 2010.

Springer,*Lecture Notes in Comp. Sci.*6502, 2011, pp. 129–140.

arXiv:1009.0088.

*J. Graph Algorithms and Applications*16 (2): 243–259, 2012.Tutte's method of spring embeddings allows any triangulated planar graph to be drawn so that the outer face has any pre-specified convex shape, but it may place vertices exponentially close to each other. Alternative graph drawing methods provide polynomial-area straight line drawings but do not allow the outer face shape to be specified. We describe a drawing method that combines both properties: it has polynomial area, and can match any pre-specified shape of the outer face, even a shape in which some of the vertices have 180 degree angles. We apply our results to drawing polygonal schemas for graphs embedded on surfaces of positive genus.

**Lombardi drawings of graphs**.

C. Duncan, D. Eppstein, M. T. Goodrich, S. Kobourov, and M. Nöllenburg.

*Proc. 18th Int. Symp. Graph Drawing*, Konstanz, Germany, 2010.

Springer,*Lecture Notes in Comp. Sci.*6502, 2011, pp. 195–207.

arXiv:1009.0579.

Invited talk at 7th Dutch Computational Geometry Day, Eindhoven, the Netherlands, 2010.

*J. Graph Algorithms and Applications*16 (1): 85–108, 2012 (special issue for GD 2010).In honor of artist Mark Lombardi, we define a Lombardi drawing to be a drawing of a graph in which the edges are drawn as circular arcs and at each vertex they are equally spaced around the vertex so as to achieve the best possible angular resolution. We describe algorithms for constructing Lombardi drawings of regular graphs, 2-degenerate graphs, graphs with rotational symmetry, and several types of planar graphs. A program for the rotationally symmetric case, the Lombardi Spirograph, is available online.

**Drawing trees with perfect angular resolution and polynomial area**.

C. Duncan, D. Eppstein, M. T. Goodrich, S. Kobourov, and M. Nöllenburg.

*Proc. 18th Int. Symp. Graph Drawing*, Konstanz, Germany, 2010.

Springer,*Lecture Notes in Comp. Sci.*6502, 2011, pp. 183–194.

arXiv:1009.0581.

*Discrete Comput. Geom.*49 (2): 157–182, 2013.We consider balloon drawings of trees, in which each subtree of the root is drawn recursively within a disk, and these disks are arranged radially around the root, with the edges at each node spaced equally around the node so as to achieve the best possible angular resolution. If we are allowed to permute the children of each node, then we show that a drawing of this type can be made in which all edges are straight line segments and the area of the drawing is a polynomial multiple of the shortest edge length. However, if the child ordering is prescribed, exponential area might be necessary. We show that, if we relax the requirement of straight line edges and draw the edges as circular arcs (a style we call Lombardi drawing) then even with a prescribed child ordering we can achieve polynomial area.

**Optimal 3D angular resolution for low-degree graphs**.

D. Eppstein, M. Löffler, E. Mumford, and M. Nöllenburg.

*Proc. 18th Int. Symp. Graph Drawing*, Konstanz, Germany, 2010.

Springer,*Lecture Notes in Comp. Sci.*6502, 2011, pp. 208–219.

arXiv:1009.0045.

*J. Graph Algorithms and Applications*17 (3): 173–200, 2013.We show how to draw any graph of maximum degree three in three dimensions with 120 degree angles at each vertex or bend, and any graph of maximum degree four in three dimensions with the angles of the diamond lattice at each vertex or bend. In each case there are no crossings and the number of bends per edge is a small constant.

**Extended dynamic subgraph statistics using**.*h*-index parameterized data structures

D. Eppstein, M. T. Goodrich, D. Strash, and L. Trott.

*Proc. 4th Int. Conf. on Combinatorial Optimization and Applications (COCOA 2010)*, Hawaii, 2010.

Springer,*Lecture Notes in Comp. Sci.*6508, 2010, pp. 128–141.

arXiv:1009.0783.

*Theor. Comput. Sci.*447: 44–52, 2012 (special issue for COCOA 2010).An earlier paper with Spiro at WADS 2009 provided dynamic graph algorithms for counting how many copies of each possible type of subgraph there are in a larger undirected graph, when the subgraphs have at most three vertices. This paper extends the method to directed graphs and to larger numbers of vertices per subgraph.

**Densities of minor-closed graph families**.

D. Eppstein.

arXiv:1009.5633.

*Electronic J. Combinatorics*17(1), Paper R136, 2010.For every minor-closed graph family (such as the family of planar graphs), there is a constant c such that the maximum number of edges in an n-vertex graph in the family is

*c*(*n*+*o*(*n*); for instance, for planar graphs,*c*= 3. We call*c*the limiting density of the family, and we study the set of all limiting densities of all minor-closed graph families. We show that this set of limiting densities is closed and well-ordered, with order type at least ω^{ω}, and we find an exact description of the members of this set up to its first two cluster points 1 and 3/2.**Listing all maximal cliques in large sparse real-world graphs**.

D. Eppstein and D. Strash.

*10th Int. Symp. Experimental Algorithms*, Crete, 2011.

Springer,*Lecture Notes in Comp. Sci.*6630, 2011, pp. 364–375.

arXiv:1103.0318.We experiment with our degeneracy-based algorithm for listing maximal cliques in sparse graphs and show that it works well on large graphs drawn from several repositories of real-world social networks and bioinformatics networks.

For the journal version, see "Listing all maximal cliques in large sparse real-world graphs", which combines results from this and a different conference paper.

**Guest editor's foreword**.

D. Eppstein and E. Gansner.

*Journal of Graph Algorithms and Applications*15 (2): 3–5, 2011.

(Special Issue on Selected Papers from the Seventeenth International Symposium on Graph Drawing, GD 2009)**Category-based routing in social networks: membership dimension and the small-world phenomenon**.

D. Eppstein, M. T. Goodrich, M. Löffler, D. Strash, and L. Trott.

*Workshop on Graph Algorithms and Applications*, Zürich, Switzerland, July 2011.

*International Conference on Computational Aspects of Social Networks (CASoN 2011)*, Salamanca, Spain, October 2011.

arXiv:1108.4675.

*Theor. Comput. Sci.*514: 96–104, 2013. (Special issue on Graph Algorithms and Applications: in Honor of Professor Giorgio Ausiello)

We investigate greedy routing schemes for social networks, in which participants know categorical information about some other participants and use it to guide message delivery by forwarding messages to neighbors that have more categories in common with the eventual destination. We define the membership dimension of such a scheme to be the maximum number of categories that any individual belongs to, a natural measure of the cognitive load of greedy routing on its participants. And we show that membership dimension is closely related to the small world phenomenon: a social network can be given a category system with polylogarithmic membership dimension that supports greedy routing if, and only if, the network has polylogarithmic diameter.

**Confluent Hasse diagrams**.

D. Eppstein and J. Simons.

*Proc. 19th Int. Symp. Graph Drawing*, Eindhoven, The Netherlands, 2011.

Springer,*Lecture Notes in Comp. Sci.*7034, 2012, pp. 2–13.

arXiv:1108.5361.

*J. Graph Algorithms and Applications*17 (7): 689–710, 2013.We show that a partial order has a non-crossing upward planar drawing if and only if it has order dimension two, and we use the Dedekind-MacNeille completion to find a drawing with the minimum possible number of confluent junctions.

**Hardness of approximate compaction for nonplanar orthogonal graph drawings**.

M. J. Bannister and D. Eppstein.

*Proc. 19th Int. Symp. Graph Drawing*, Eindhoven, The Netherlands, 2011.

Springer,*Lecture Notes in Comp. Sci.*7034, 2012, pp. 367–378.We show that, for several variants of the problem of compacting a grid drawing of a graph to use the minimum number of rows or minimum area, no good approximation algorithm is possible. We also develop fixed-parameter tractable algorithms and approximation algorithms showing that some of our inapproximability bounds are tight. See the journal version, "Inapproximability of orthogonal compaction", for some improvements and corrections.

**Planar and poly-arc Lombardi drawings**.

C. Duncan, D. Eppstein, M. T. Goodrich, S. Kobourov, and M. Löffler, and M. Nöllenburg.

*Proc. 19th Int. Symp. Graph Drawing*, Eindhoven, The Netherlands, 2011.

Springer,*Lecture Notes in Comp. Sci.*7034, 2012, pp. 308–319.

arXiv:1109.0345.

*J. Computational Geometry*9 (1): 328–355, 2018.We extend Lombardi drawing (in which each edge is a circular arc and the edges incident to a vertex must be equally spaced around it) to drawings in which edges are composed of multiple arcs, and we investigate the graphs that can be drawn in this more relaxed framework.

**Randomized speedup of the Bellman–Ford algorithm**.

M. J. Bannister and D. Eppstein.

arXiv:1111.5414.

*Analytic Algorithmics and Combinatorics (ANALCO12)*, Kyoto, Japan, 2012, pp. 41–47.The Bellman–Ford algorithm for single-source shortest paths in graphs that may have negatively weighted edges but no negative cycles can be sped up by a technique of Yen in which the graph is partitioned into two directed acyclic subgraphs and edge relaxations alternate between these two subgraphs. We show that choosing this partition randomly gains an additional factor of 2/3 in running time.

**Inapproximability of orthogonal compaction**.

M. J. Bannister, D. Eppstein, and J. Simons.

arXiv:1108.4705.

*J. Graph Algorithms and Applications*16 (3): 651–673, 2012. (Special issue for GD 2011.)This is the journal version of "Hardness of approximate compaction for nonplanar orthogonal graph drawings". It has stronger inapproximability bounds, and more variations of the compaction problem that are hard to approximate. In addition it includes a retraction of a buggy approximation algorithm from the conference version.

**Area-universal and constrained rectangular layouts**.

D. Eppstein, E. Mumford, B. Speckmann, and K. Verbeek.

*SIAM J. Computing*41 (3): 537–564, 2012.A combined journal version of "Area-universal rectangular layouts" and "Orientation-constrained rectangular layouts".

**Solving single-digit Sudoku subproblems**.

D. Eppstein.

arXiv:1202.5074.

*6th International Conference on Fun with Algorithms (FUN 2012)*, Venice, Italy, 2012.

Springer,*Lecture Notes in Comp. Sci.*7288, 2012, pp. 142–153.We find an algorithm for making all possible deductions based on the set of candidate locations for a single digit in a Sudoku puzzle; the problem is NP-hard, and our algorithm takes exponential time, but the mild form of the exponential allows it to be fast for practical problem sizes.

(Slides)

**Near-linear-time deterministic plane Steiner spanners and TSP approximation for well-spaced point sets**.

G. Borradaile and D. Eppstein.

arXiv:1206.2254.

*24th Canadian Conference on Computational Geometry (CCCG 2012)*, Prince Edward Island, Canada, 2012, pp. 311–316.

*Comp. Geom. Theory & Applications*49: 8–16, 2015 (special issue for CCCG 2012).When a planar point set has the property that its Delaunay triangulation has no large angles, we show how to connect it by a plane graph (having linearly many additional Steiner vertices) in which the distances between the original points are approximations to their Euclidean distance, and in which the total graph weight is at most a constant times the minimum spanning tree weight. The time to construct this graph is near-linear, the same as for integer sorting. We use this result to approximate the traveling salesman problem, for these point sets, in the same time bound.

**Planar Lombardi drawings for subcubic graphs**.

D. Eppstein.

arXiv:1206.6142.

*20th Int. Symp. Graph Drawing*, Redmond, Washington, 2012.

Springer,*Lecture Notes in Comp. Sci.*7704, 2013, pp. 126–137.

We show that every planar graph of maximum degree three has a planar Lombardi drawing and that some but not all 4-regular planar graphs have planar Lombardi drawings. The proof idea combines circle packings with a form of Möbius-invariant power diagram for circles, defined using three-dimensional hyperbolic geometry.

For the journal version, see "A Möbius-invariant power diagram and its applications to soap bubbles and planar lombardi drawing.".

(Slides)

**Force-directed graph drawing using social gravity and scaling**.

M. J. Bannister, D. Eppstein, M. T. Goodrich, and L. Trott.

arXiv:1209.0748.

*20th Int. Symp. Graph Drawing*, Redmond, Washington, 2012.

Springer,*Lecture Notes in Comp. Sci.*7704, 2013, pp. 414–425.

We extend force-directed methods of graph drawing by adding a force that pulls vertices towards the center of the drawing, with a strength proportional to the centrality of the vertex. Gradually scaling up this force helps avoid the tangling that would otherwise result from its use.

**On the density of maximal 1-planar graphs**.

F. J. Brandenburg, D. Eppstein, A. Gleißner, M. T. Goodrich, K. Hanauer, and J. Reislhuber.

*20th Int. Symp. Graph Drawing*, Redmond, Washington, 2012.

Springer,*Lecture Notes in Comp. Sci.*7704, 2013, pp. 327–338.

A graph is 1-planar if it can be drawn in the plane with at most one crossing per edge, and maximal 1-planar if it is 1-planar but adding any edge would force more than one crossing on some edge or edges. Although maximal 1-planar graphs on

*n*vertices may have as many as 4*n*− 8 edges, we show that there exist maximal 1-planar graphs with as few as 45*n*/17 + O(1) edges.**Windows into relational events: data structures for contiguous subsequences of edges**.

M. J. Bannister, C. DuBois, D. Eppstein, and P. Smyth.

*NIPS 2012 Workshop on Algorithmic and Statistical Approaches for Large Social Networks*, South Lake Tahoe, California, 2012 (poster and invited talk).

*24th ACM-SIAM Symp. Discrete Algorithms*, New Orleans, Louisiana, 2013, pp. 856–864.

arXiv:1209.5791.We study relational event data in which a collection of actors in a social network have a sequence of pairwise interactions. Contiguous subsequences of these interactions form graphs, and we develop efficient data structures for querying the parameters of these graphs.

**The graphs of planar soap bubbles**.

D. Eppstein.

arXiv:1207.3761.

*Proc. 29th ACM Symp. on Computational Geometry*, Rio de Janeiro, 2013, pp. 27–36.We characterize the graphs of two-dimensional soap bubble clusters as being exactly the bridgeless 3-regular planar graphs. The proof uses the Möbius invariance of the properties characterizing these clusters together with our previous circle packing method for constructing Lombardi drawings of graphs.

For the journal version, see "A Möbius-invariant power diagram and its applications to soap bubbles and planar lombardi drawing.".

(Slides)

**Antimatroids and balanced pairs**.

D. Eppstein.

arXiv:1302.5967.

*Order*31 (1): 81–99, 2014. Erratum (with V. Wiechert).We generalize the 1/3-2/3 conjecture, according to which every partial order should have a pair of items that are nearly equally likely to appear in either order in a random linear extension, to antimatroids, and we prove it for several specific types of antimatroid.

**Grid minors in damaged grids**.

D. Eppstein.

arXiv:1303.1136.

*Electronic J. Combinatorics*21(3), Paper P3.20, 2014.We give tight bounds on the size of the largest remaining grid minor in a grid graph from which a given number of vertices have been deleted, and study several related problems.

**Parameterized complexity of 1-planarity**.

M. J. Bannister, S. Cabello, and D. Eppstein.

arXiv:1304.5591.

13th Int. Symp. Algorithms and Data Structures (WADS 2013), London, Ontario

Springer,*Lecture Notes in Comp. Sci. 8037*, 2013, pp. 97–108.

*J. Graph Algorithms and Applications*22 (1): 23–49, 2018. (Special issue on Graph Drawing Beyond Planarity.)

We show that testing whether a graph is 1-planar (drawable with at most one crossing per edge) may be performed in polynomial and fixed-parameter tractable time for graphs of bounded circuit rank, vertex cover number, or tree-depth. However, it is NP-complete for graphs of bounded treewidth, pathwidth, or bandwidth.

(Slides)

**Knowledge Spaces: Applications in Education**.

J.-C. Falmagne, D. Albert, C. Doble, D. Eppstein, and X. Hu, eds.

Springer, 2013.This edited volume collects experiences with automated learning systems based on the theory of knowledge spaces, and mathematical explorations of the theory of knowledge spaces and their efficient implementation.

**Learning sequences: an efficient data structure for learning spaces**.

D. Eppstein.

In*Knowledge Spaces: Applications in Education*, J.-C. Falmagne, D. Albert, C. Doble, D. Eppstein, and X. Hu, eds.

Springer, 2013, pp. 287–304.We show how to represent a learning space by a small family of learning sequences, orderings of the items in a learning sequence that are consistent with their prerequisite relations. This representation allows for the rapid generation of the family of all consistent knowledge states and the efficient assessment of the state of knowledge of a human learner.

**Projection, decomposition, and adaption of learning spaces**.

D. Eppstein.

In*Knowledge Spaces: Applications in Education*, J.-C. Falmagne, D. Albert, C. Doble, D. Eppstein, and X. Hu, eds.

Springer, 2013, pp. 305–322.In another chapter of the same book we used learning sequences to represent learning spaces and perform efficient knowledge assessment of a human learning. In this chapter we show how to use the same data structure to build learning spaces on a sample of the items of a larger learning space (an important subroutine in knowledge assessment) and to modify a learning space to more accurately model students.

**A brief history of curves in graph drawing**.

D. Eppstein.

Invited survey talk at Workshop on Drawing Graphs and Maps with Curves, Dagstuhl, Germany, April 2013.

*Drawing Graphs and Maps with Curves (Dagstuhl Seminar 13151)*, S. G. Kobourov, M. Nöllenburg, and M. Teillaud, eds., Dagstuhl Reports 3(4): 40–46, 2013.(Slides)

**Universal point sets for planar graph drawings with circular arcs**.

P. Angelini, D. Eppstein, F. Frati, M. Kaufmann, S. Lazard, T. Mchedlidze, M. Teillaud, and A. Wolff.

HAL-Inria open archive oai:hal.inria.fr:hal-00846953.

*25th Canadian Conference on Computational Geometry*, Waterloo, Canada, 2013.

*J. Graph Algorithms and Applications*18 (3): 313–324, 2014.For every positive integer

*n*, there exists a set of*n*points on a parabola, with the property that every*n*-vertex planar graph can be drawn without crossings with its vertices at these points and with its edges drawn as circular arcs.(Slides)

**Fixed parameter tractability of crossing minimization of almost-trees**.

M. J. Bannister, D. Eppstein, and J. Simons.

arXiv:1308.5741.

*21st Int. Symp. Graph Drawing*, Bordeaux, France, 2013.

Springer,*Lecture Notes in Comp. Sci.*8242, 2013, pp. 340–351.

Many real-world graphs are k-almost-trees for small values of k: graphs in which, in every biconnected component, removing a spanning tree leaves at most k edges. We use kernelization methods to show that in such graphs, the 1-page and 2-page crossing numbers can be computed quickly.

**Superpatterns and universal point sets**.

M. J. Bannister, Z. Cheng, W. E. Devanny, and D. Eppstein.

arXiv:1308.0403.

*21st Int. Symp. Graph Drawing*, Bordeaux, France, 2013.

Springer,*Lecture Notes in Comp. Sci.*8242, 2013, pp. 208–219.

Bannister's talk on this paper won the GD2013 best presentation award.

*J. Graph Algorithms & Applications*18 (2): 177–209, 2014 (special issue for GD'13).A superpattern of a set of permutations is a permutation that contains as a pattern every permutation in the set. Previously superpatterns had been considered for all permutations of a given length; we generalize this to sets of permutations defined by forbidden patterns; we show that the 213-avoiding permutations have superpatterns half the length of the known bound for all permutations, and that any proper permutation subclass of the 213-avoiding permutations has near-linear superpatterns. We apply these results to the construction of universal point sets, sets of points that can be used as the vertices of drawings of all n-vertex planar graphs. We use our 213-avoiding superpatterns to construct universal sets of size approximately

*n*^{2}/4, and we also construct near-linear universal sets for graphs of bounded pathwidth.**Drawing arrangement graphs in small grids, or how to play planarity**.

D. Eppstein.

arXiv:1308.0066.

*21st Int. Symp. Graph Drawing*, Bordeaux, France, 2013.

Springer,*Lecture Notes in Comp. Sci.*8242, 2013, pp. 436–447.

*J. Graph Algorithms & Applications*18 (2): 211–231, 2014 (special issue for GD'13).The planarity game involves rearranging a scrambled line arrangement graph to make it planar. We show that the resulting graphs have drawings in grids of area

*n*^{7/6}, much smaller than the quadratic size bound for grid drawings of planar graphs, and we provide a strategy for planarizing these graphs that is simple enough for human puzzle solving.**Strict confluent drawing**.

D. Eppstein, D. Holten, M. Löffler, M. Nöllenburg, and B. Speckmann, and K. Verbeek.

arXiv:1308.6824.

*21st Int. Symp. Graph Drawing*, Bordeaux, France, 2013.

Springer,*Lecture Notes in Comp. Sci.*8242, 2013, pp. 352–363.

*J. Computational Geometry*7 (1): 22–46, 2016.A confluent drawing of a graph is a set of points and curves in the plane with the property that two vertices are adjacent in the graph if and only if the corresponding points can be connected to each other by smooth paths in the drawing. We define a variant of confluent drawing, strict confluent drawing, in which a smooth path between two vertices (if it exists) must be unique. We show that it is NP-complete to test whether such drawings exist, in contrast to unrestricted confluence for which the complexity remains open. Additionally, we show that finding outerplanar drawings (in which the points are on the boundary of a disk and the curves are interior to it) with a fixed cyclic vertex ordering can be performed in polynomial time. We use circle packings to find nice versions of these drawings in which all tracks are represented by piecewise-circular curves.

**Convex-arc drawings of pseudolines**.

D. Eppstein, M. van Garderen, B. Speckmann, and T. Ueckerdt.

*21st Int. Symp. Graph Drawing*(poster), Bordeaux, France, 2013.

Springer,*Lecture Notes in Comp. Sci.*8242, 2013, pp. 522–523.

arXiv:1601.06865.

We show that every outerplanar weak pseudoline arrangement (a collection of curves topologically equivalent to lines, each crossing at most once but possibly zero times, with all crossings belonging to an infinite face) can be straightened to a hyperbolic line arrangement. As a consequence such an arrangement can also be drawn in the Euclidean plane with each pseudoline represented as a convex piecewise-linear curve with at most two bends. In contrast, for arbitrary pseudoline arrangements, a linear number of bends is sufficient and sometimes necessary.

**Small superpatterns for dominance drawing**.

M. J. Bannister, W. E. Devanny, and D. Eppstein.

arXiv:1310.3770.

*Analytic Algorithmics and Combinatorics (ANALCO14)*, Portland, Oregon, 2014, pp. 92–103.We construct small universal point sets for dominance drawings of classes of acyclic graphs, by finding forbidden patterns in the permutations determined by these drawings and proving the existence of small superpatterns for the permutations with these patterns forbidden. In particular, dominance drawings of the Hasse diagrams of width-2 partial orders have universal point sets of size O(

*n*^{3/2}), derived from superpatterns of the same size for the 321-avoiding permutations, and dominance drawings of st-planar graphs have universal point sets of size O(*n*log*n*), derived from superpatterns for riffle shuffles.**Structures in solution spaces: Three lessons from Jean-Claude**.

D. Eppstein.

Invited talk, Conference on Meaningfulness and Learning Spaces: A Tribute to the Work of Jean-Claude Falmagne

Irvine, California, 2014.This talk surveys my work on rectangular cartograms, the 1/3-2/3 conjecture for antimatroids, and flip distance for triangulations of point sets with no empty pentagon, and how this line of research stemmed from the work of Jean-Claude Falmagne on learning spaces.

**Listing all maximal cliques in large sparse real-world graphs**.

D. Eppstein, M. Löffler, and D. Strash.

*J. Experimental Algorithmics*18 (3): 3.1, 2013 (special issue for SEA).This paper combines our theoretical results on clique-finding algorithms from ISAAC 2010 with our experimental results on the same algorithms from SEA 2011. We show how to list all maximal cliques in graphs of bounded degeneracy in time that is linear in the size of the graph and near-optimal in the degeneracy, and we show that low degeneracy explains the good behavior of the algorithm in our experiments on large real-world social networks.

**Automated generation of linkage loop equations for planar 1-dof linkages, demonstrated up to 8-bar**.

B. E. Parrish, J. M. McCarthy, and D. Eppstein.

*Proc. ASME 2014 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference*, Vol. 5A:*38th Mechanisms and Robotics Conference*, Buffalo, New York, USA, August 17-20, 2014, paper no. DETC2014-35263.

*J. Mechanisms and Robotics*7 (1): 011006, 2015.This paper reports on an implementation of an algorithm for constructing the configuration space of two-dimensional linkages with one degree of freedom.

(eScholarship conference version – eScholarship journal version)

**Planar induced subgraphs of sparse graphs**.

G. Borradaile, D. Eppstein, and P. Zhu.

arXiv:1408.5939.

*22nd Int. Symp. Graph Drawing*, Würzburg, Germany, 2014.

Springer,*Lecture Notes in Comp. Sci.*8871, 2014, pp. 1–12.

*J. Graph Algorithms & Applications*19 (1): 281–297, 2015.We investigate the number of vertices that must be deleted from an arbitrary graph, in the worst case as a function of the number of edges, in order to planarize the remaining graph. We show that

*m*/5.22 vertices are sufficient and*m*/(6 − o(1)) are necessary, and we also give bounds for the number of deletions needed to achieve certain subclasses of planar graphs.**The Galois complexity of graph drawing: why numerical solutions are ubiquitous for force-directed, spectral, and circle packing drawings**.

M. J. Bannister, W. E. Devanny, D. Eppstein, and M. T. Goodrich.

arXiv:1408.1422.

*22nd Int. Symp. Graph Drawing*, Würzburg, Germany, 2014

Springer,*Lecture Notes in Comp. Sci.*8871, 2014, pp. 149–161.

*J. Graph Algorithms & Applications*19 (2): 619–656, 2015 (special issue for GD'14).We show that many standard graph drawing methods have algebraic solutions described by polynomials that can have unsolvable Galois groups, and that can have Galois groups whose order is divisible by large prime numbers. As a consequence certain models of exact algebraic computation are unable to construct these drawings.

**Crossing minimization for 1-page and 2-page drawings of graphs with bounded treewidth**.

M. J. Bannister and D. Eppstein.

arXiv:1408.6321.

*22nd Int. Symp. Graph Drawing*, Würzburg, Germany, 2014.

Springer,*Lecture Notes in Comp. Sci.*8871, 2014, pp. 210–221.

*J. Graph Algorithms & Applications*22 (4): 577–606, 2018.We show how to express in monadic second-order logic the problems of drawing a graph with a fixed number of crossings on a one or two page book layout. By applying Courcelle's theorem, we obtain fixed-parameter tractable algorithms for these problems, parameterized by treewidth.

**Balanced circle packings for planar graphs**.

M. J. Alam, D. Eppstein, M. T. Goodrich, S. Kobourov, and S. Pupyrev.

arXiv:1408.4902.

*22nd Int. Symp. Graph Drawing*, Würzburg, Germany, 2014.

Springer,*Lecture Notes in Comp. Sci.*8871, 2014, pp. 125–136.The balanced circle packings of the title are systems of interior-disjoint circles, whose tangencies represent the given graph, and whose radii are all within a polynomial factor of each other. We show that these packings always exist for trees, cactus graphs, outerpaths, k-outerplanar graphs of bounded degree when k is at most logarithmic, and planar graphs of bounded treedepth. The treedepth result uses a new construction of inversive-distance circle packings.

**Flat foldings of plane graphs with prescribed angles and edge lengths**.

Z. Abel, E. Demaine, M. Demaine, D. Eppstein, A. Lubiw, and R. Uehara.

arXiv:1408.6771.

*22nd Int. Symp. Graph Drawing*, Würzburg, Germany, 2014.

Springer,*Lecture Notes in Comp. Sci.*8871, 2014, pp. 272–283.

*J. Computational Geometry*9 (1): 74–93, 2018.Given a plane graph with fixed edge lengths, and an assignment of the angles 0, 180, and 360 to the angles between adjacent edges, we show how to test whether the angle assignment can be realized by an embedding of the graph as a flat folding on a line. As a consequence, we can determine whether two-dimensional cell complexes with one vertex can be flattened. The main idea behind the result is to show that each face of the graph can be folded independently of the other faces.

.*k*-best enumeration

D. Eppstein.

*Encyclopedia of Algorithms*(Ming-Yang Kao, ed.), Springer, added 2014.

arXiv:1412.5075.

*Bull. EATCS*115, 2015.A brief survey of algorithms for finding the

*k*shortest paths and related*k*-best enumeration problems. The arXiv/EATCS version is significantly longer and with more references than the Springer version.**Minimum forcing sets for Miura folding patterns**.

B. Ballinger, M. Damian, D. Eppstein, R. Flatland, J. Ginepro, and T. Hull.

arXiv:1410.2231.

*26th ACM-SIAM Symp. on Discrete Algorithms*, San Diego, 2015, pp. 136–147.A forcing set for an origami crease pattern is a subset of the folds with the property that, if these folds are folded the correct way (mountain vs valley) the rest of the pattern also has to be folded the correct way. We use a combinatorial equivalence with three-colored grids to construct minimum-cardinality forcing sets for the Miura-ori folding pattern and for other patterns with differing folds along the same line segments.

(Slides)

**All-pairs minimum cuts in near-linear time for surface-embedded graphs**.

G. Borradaile, D. Eppstein, A. Nayyeri, and C. Wulff-Nilsen.

arXiv:1411.7055.

*Proc. 32nd Int. Symp. Computational Geometry*, Boston, 2016.

Leibniz International Proceedings in Informatics (LIPIcs) 51, pp. 22:1–22:16.

We give the first known near-linear algorithms for constructing Gomory–Hu trees of bounded-genus graphs, and we shave a log off the time for the same problem on planar graphs.

**ERGMs are hard**.

M. J. Bannister, W. E. Devanny, and D. Eppstein.

arXiv:1412.1787.

ERGMs (exponential random graph models) are used in social science to describe probability distributions on graphs that are supposed to mimic real-world social networks. However, we show that (with features that are standard in the social science application) the distributions given by these models can be computationally infeasible to sample from or to approximate the probability of seeing a given graph.

**Contact graphs of circular arcs**.

M. J. Alam, D. Eppstein, M. Kaufmann, S. Kobourov, S. Pupyrev A. Schulz, and T. Ueckerdt.

arXiv:1501.00318.

14th Algorithms and Data Structures Symp. (WADS 2015), Victoria, BC.

Springer,*Lecture Notes in Comp. Sci.*9214 (2015), pp. 1–13.We study the graphs formed by non-crossing circular arcs in the plane, having a vertex for each arc and an edge for each point where an arc endpoint touches the interior of another arc.

(Slides)

**Simple recognition of Halin graphs and their generalizations**.

D. Eppstein.

arXiv:1502.05334.

*J. Graph Algorithms & Applications*20 (2): 323–346, 2016.We describe and implement a simple linear time algorithm for recognizing Halin graphs based on two simplifications of triples of degree-three vertices in such graphs. Removing some auxiliary data from the algorithm causes it to recognize a broader class of graphs that we call the D3-reducible graphs. We study the properties of these graphs, showing that they share many properties with the Halin graphs.

**Rooted cycle bases**.

D. Eppstein, J. M. McCarthy, and B. E. Parrish.

arXiv:1504.04931.

14th Algorithms and Data Structures Symp. (WADS 2015), Victoria, BC.

Springer,*Lecture Notes in Comp. Sci.*9214 (2015), pp. 339–350.

*J. Graph Algorithms & Applications*21 (4): 663–686, 2017.We consider the problem of finding a cycle basis for a graph in which all basis cycles contain a specified edge. We characterize the graphs having such a basis in terms of their vertex connectivity, we show that the minimum weight cycle basis with this constraint can be found in polynomial time and is weakly fundamental, and we show that finding a fundamental cycle basis with this constraint is NP-hard but fixed-parameter tractable.

(Slides)

**The parametric closure problem**.

D. Eppstein.

arXiv:1504.04073.

14th Algorithms and Data Structures Symp. (WADS 2015), Victoria, BC.

Springer,*Lecture Notes in Comp. Sci.*9214 (2015), pp. 327–338.

*ACM Trans. Algorithms*14 (1): Article 2, 2018.We consider the minimum weight closure problem for a partially ordered set whose elements have weights that vary linearly as a function of a parameter. For several important classes of partial orders the number of changes to the optimal solution as the parameter varies is near-linear, and the sequence of optimal solutions can be found in near-linear time.

(Slides)

**Metric dimension parameterized by max leaf number**.

D. Eppstein.

arXiv:1506.01749.

*J. Graph Algorithms & Applications*19 (1): 313–323, 2015.We prove that when a graph of bounded size has its edges subdivided to form a larger graph, it is still possible to find its metric dimension by a fixed-parameter tractable algorithm, parameterized by the pre-subdivision size of the graph.

**Structure of graphs with locally restricted crossings**.

V. Dujmović, D. Eppstein, and D. R. Wood.

arXiv:1506.04380.

*23rd Int. Symp. Graph Drawing*, Los Angeles, California, 2015.

Springer,*Lecture Notes in Comp. Sci.*9411 (2015), pp. 87–98.

*SIAM J. Discrete Math.*31 (2): 805–824, 2017.The Graph Drawing version used the alternative title "Genus, treewidth, and local crossing number". We prove tight bounds on the treewidth of graphs embedded on low-genus surfaces with few crossings per edge, and nearly tight bounds on the number of crossings per edge for graphs with a given number of edges embedded on low-genus surfaces.

(Slides — local copy of final version)

**Track layouts, layered path decompositions, and leveled planarity**.

M. J. Bannister, W. E. Devanny, and V. Dujmović, D. Eppstein, and D. R. Wood.

arXiv:1506.09145.

*24th Int. Symp. Graph Drawing*, Athens, Greece, 2016.

Springer,*Lecture Notes in Comp. Sci.*9801 (2016), pp. 499–510.

*Algorithmica*81 (4): 1561–1583, 2019.We introduce the concept of a layered path decomposition, and show that the layered pathwidth can be used to characterize the leveled planar graphs. As a consequence we show that finding the minimum number of tracks in a track layout of a given graph is NP-complete. The GD version includes only the parts concerning track layout, and uses the title "Track Layout is Hard".

**Approximate greedy clustering and distance selection for graph metrics**.

D. Eppstein, S. Har-Peled, and A. Sidiropoulos.

arXiv:1507.01555.

*J. Computational Geometry*11 (1): 629–652, 2020.We provide fast approximation algorithms for the farthest-first traversal of graph metrics.

**Confluent orthogonal drawings of syntax diagrams**.

M. J. Bannister, D. A. Brown, and D. Eppstein.

arXiv:1509.00818.

*23rd Int. Symp. Graph Drawing*, Los Angeles, California, 2015.

Springer,*Lecture Notes in Comp. Sci.*9411 (2015), pp. 260–271.We describe a system for transforming context-free grammars into human-readable syntax diagrams, including optimizations that change the structure of the grammar to make it more readable without affecting the language described by the grammar.

**Treetopes and their graphs**.

D. Eppstein.

arXiv:1510.03152.

*27th ACM-SIAM Symp. on Discrete Algorithms*, Arlington, 2016, pp. 969–984.

*Discrete Comput. Geom.*64 (2), 259–289, 2020 (special issue for Branko Grünbaum).

We describe a class of polytopes of varying dimensions, whose restriction to three dimensions is the class of roofless polyhedra (Halin graphs). We call these polytopes treetopes. We show that the four-dimensional treetopes are closely related to clustered planar graph drawings, and we use this connection to recognize the graphs of four-dimensional treetopes in polynomial time.

(Slides)

**On the planar split thickness of graphs**.

D. Eppstein, P. Kindermann, S. G. Kobourov, G. Liotta, A. Lubiw, A. Maignan, D. Mondal, H. Vosoughpour, S. Whitesides, and S. Wismath.

arXiv:1512.04839.

*Proc. 12th Latin American Theoretical Informatics Symposium (LATIN 2016)*, Ensenada, Mexico.

Springer,*Lecture Notes in Comp. Sci.*9644 (2016), pp. 403–415.

*Algorithmica*80 (3): 977–994 (special issue for LATIN), 2018.We study the problem of splitting the vertices of a given graph into a bounded number of sub-vertices (with each edge attaching to one of the sub-vertices) in order to make the resulting graph planar. It is NP-complete, but can be approximated to within a constant factor, and is fixed-parameter tractable in the treewidth.

(Slides)

**The computational hardness of**.*d*K-series

W. E. Devanny, D. Eppstein, and B. Tillman.

*NetSci2016*poster session, Seoul, Korea.The

*d*K-series is an extension of the degree sequence of a graph to a*d*-dimensional tensor, describing the number of*d*-tuples of vertices with each possible combination of degrees and adjacencies. As we show, it is NP-hard to determine whether such a tensor represents a valid graph, for any*d*≥ 3, or for*d*= 2 if the number of triangles in the graph is also specified (or constrained to be zero).**Models and algorithms for graph watermarking**.

D. Eppstein, M. T. Goodrich, J. Lam, N. Mamano, M. Mitzenmacher, and M. Torres.

arXiv:1605.09425.

*Proc. 19th Information Security Conference (ISC 2016)*, Honolulu, Hawaii.

Springer,*Lecture Notes in Comp. Sci.*9866 (2016), pp. 283–301.We show how to modify a small number of edges in a large social network in order to make the modified copy easy to identify, even if an adversary tries to hide the modification by permuting the vertices and flipping a much larger number of edges. The result depends on the random fluctuation of vertex degrees in such networks, and the ability to uniquely identify vertices by their adjacencies to a small number of high-degree landmark vertices. This paper won the best student paper award at ISC for its student co-authors Lam, Mamano, and Torres.

.*K*-best solutions of MSO problems on tree-decomposable graphs

D. Eppstein and D. Kurz.

arXiv:1703.02784.

*Proc. 12th International Symposium on Parameterized and Exact Computation (IPEC 2017)*, Vienna, Austria, 2017.

Leibniz International Proceedings in Informatics (LIPIcs) 89, pp. 16.1–16.13We show that, on graphs of bounded treewidth, for any optimization problem definable in monadic second-order logic, we can find the

*k*best solutions in logarithmic time per solution.**Algorithms for stable matching and clustering in a grid**.

D. Eppstein, M. T. Goodrich, and N. Mamano.

arXiv:1704.02303

*Proc. 18th International Workshop on Combinatorial Image Analysis (IWCIA 2017)*, Plovdiv, Bulgaria, 2017.

Springer,*Lecture Notes in Comp. Sci.*10256 (2017), pp. 117–131.Motivated by redistricting, we consider geometric variants of the stable matching problem in which points (such as the pixels of a discretization of the unit square) are to be matched to a smaller number of centers such that each center has the same number of matches and no match is unstable with respect to Euclidean distances. We show how to solve such problems in polylogarithmic time per matched point, experiment with practical heuristics for solving these problems, and test methods for moving the centers to improve the shape of the matched regions.

**2-3 cuckoo filters for faster triangle listing and set intersection**.

D. Eppstein, M. T. Goodrich, M. Mitzenmacher, and M. Torres.

*Proc. 36th ACM SIGMOD-SIGACT-SIGAI Symposium on Principles of Database Systems (PODS 2017)*, Chicago, 2017, pp. 247–260.

We show that bit-parallel algorithm design techniques, on a machine of word size

*w*, can speed up the time for sparse set intersection by a factor of log*w*/*w*. The main data structure underlying our algorithms is the cuckoo filter, a variant of cuckoo hash tables that has operations similar to a Bloom filter but outperforms Bloom filters in several respects.**Defining equitable geographic districts in road networks via stable matching**.

D. Eppstein, M. T. Goodrich, D. Korkmaz, and N. Mamano.

arXiv:1706.09593

*Proc. 25th ACM SIGSPATIAL Int. Conf. Advances in Geographic Information Systems (ACM SIGSPATIAL 2017)*, Redondo Beach, California, pp. 52:1–52:4.

We cluster road networks (modeled as planar graphs, or more generally as graphs obeying a separator theorem) with a given set of cluster centers, by matching graph vertices to centers stably according to distance: no unmatched vertex and center should have smaller distances than the matched pairs for the same points. We provide a separator-based data structure for dynamic nearest neighbor queries in planar or separated graphs, which allows the optimal stable clustering to be constructed in time

*O*(*n*^{3/2}log*n*). We also experiment with heuristics for fast practical construction of this clustering.**Triangle-free penny graphs: degeneracy, choosability, and edge count**.

D. Eppstein.

arXiv:1708.05152.

*Proc. 25th Int. Symp. Graph Drawing*, Boston, Massachusetts, 2017.

Springer,*Lecture Notes in Comp. Sci.*10692 (2018), pp. 506–513.

*J. Graph Algorithms & Applications*22 (3): 483–499 (special issue for GD 2017), 2018.A penny graph is the contact graph of unit disks: each disk represents a vertex of the graph, no two disks can overlap, and each tangency between two disks represents an edge in the graph. We prove that, when this graph is triangle free, its degeneracy is at most two. As a consequence, triangle-free penny graphs have list chromatic number at most three. We also show that the number of edges in any such graph is at most 2

*n*− Ω(√*n*). The journal version uses the alternative title "Edge Bounds and Degeneracy of Triangle-Free Penny Graphs and Squaregraphs".(Slides)

**The effect of planarization on width**.

D. Eppstein.

arXiv:1708.05155.

*Proc. 25th Int. Symp. Graph Drawing*, Boston, Massachusetts, 2017.

Springer,*Lecture Notes in Comp. Sci.*10692 (2018), pp. 560–572.

*J. Graph Algorithms & Applications*22 (3): 461–481 (special issue for GD 2017), 2018.We study what happens to nonplanar graphs of low width (for various width measures) when they are made planar by replacing crossings by vertices. For treewidth, pathwidth, branchwidth, clique-width, and tree-depth, this replacement can blow up the width from constant to linear. However, for bandwidth, cutwidth, and carving width, graphs of bounded width stay bounded when we planarize them.

(Slides)

**Crossing patterns in nonplanar road networks**.

D. Eppstein and S. Gupta.

arXiv:1709.06113.

*Proc. 25th ACM SIGSPATIAL Int. Conf. Advances in Geographic Information Systems (ACM SIGSPATIAL 2017)*, Redondo Beach, California, pp. 40:1–40:9.

We show that, although an individual edge in a road network can have many crossings, real-world road networks have the property that the crossing graph of their edges is sparse. We prove that networks with this property are themselves sparse and have small separators, allowing many fast algorithms to be generalized from planar graphs to these networks.

**Square-contact representations of partial 2-trees and triconnected simply-nested graphs**.

G. Da Lozzo, W. E. Devanny, D. Eppstein, and T. Johnson.

arXiv:1710.00426.

*Proc. 28th Int. Symp. Algorithms and Computation (ISAAC 2017)*, Phuket, Thailand, 2017.

Leibniz International Proceedings in Informatics (LIPIcs) 92, pp. 24:1–24:16.

We show that the

*K*_{1,1,3}-free partial 2-trees and the Halin graphs other than*K*_{4}can all be represented as proper contact graphs of squares in the plane. Among partial 2-trees and Halin graphs, these are exactly the ones that can be embedded without nonempty triangles, which form an obstacle to the existence of square contact representations. However the graph of a square antiprism has no such representation despite being embeddable without any nonempty triangles.**NC algorithms for perfect matching and maximum flow in one-crossing-minor-free graphs**.

D. Eppstein and V. V. Vazirani.

arXiv:1802.00084.

*Proc. 30th ACM Symposium on Parallelism in Algorithms and Architectures (SPAA 2019)*, Phoenix, Arizona, 2019, pp. 23–30.

*SIAM J. Computing*50 (3): 1014–1033, 2021.We extend Anari and Vazirani's parallel algorithm for perfect matching in planar graphs to the graph families with a forbidden minor with crossing number one, by developing a concept of mimicking networks for perfect matching.

(Slides)

**Reactive proximity data structures for graphs**.

D. Eppstein, M. T. Goodrich, and N. Mamano.

arXiv:1803.04555.

*Proc. 13th Latin American Theoretical Informatics Symposium (LATIN 2018)*, Buenos Aires, Argentina.

Springer,*Lecture Notes in Comp. Sci.*10807 (2018), pp. 777–789.We develop data structures for solving nearest neighbor queries for dynamic subsets of vertices in a planar graph, or more generally for a graph in any graph class with small separators (polynomial expansion).

**Subexponential-time and FPT algorithms for embedded flat clustered planarity**.

G. Da Lozzo, D. Eppstein, M. T. Goodrich, and S. Gupta.

arXiv:1803.05465

*Proc. 44th International Workshop on Graph-Theoretic Concepts in Computer Science (WG 2018)*, Lübbenau, Germany.

Springer,*Lecture Notes in Comp. Sci.*11159 (2018), pp. 111–124.Clustered planarity is the problem of simultaneously drawing a planar graph and a clustering of its vertices (as Jordan curves surrounding the cluster) with no unnecessary crossings between edges or cluster boundaries; it remains unknown whether it can be solved in polynomial time. We provide parameterized and subexponential exact algorithms for the case where the planar embedding is fixed and the clusters form a partition of the vertices.

**Parameterized leaf power recognition via embedding into graph products**.

D. Eppstein and E. Havvaei.

arXiv:1810.02452.

*Proc. 13th International Symposium on Parameterized and Exact Computation (IPEC 2018)*, Helsinki, Finland, 2018.

Leibniz International Proceedings in Informatics (LIPIcs) 115, 2018, pp. 16:1–16:14.

*Algorithmica*82 (8): 2337–2359, 2020 (special issue for IPEC 2018).A leaf power graph is the graph formed from the leaves of a tree by making two leaves adjacent when their tree distance is at most

*k*. We show that recognizing these graphs is fixed-parameter tractable in a combination of two parameters:*k*and the degeneracy of the graph.(James Nastos has pointed out a minor error in our statement of known prior results: the figure depicting chordal graphs that are not 4-leaf powers is labeled as a complete set of forbidden subgraphs, but it is only the complete set among graphs without true twin vertices.)

**Realization and connectivity of the graphs of origami flat foldings**.

D. Eppstein.

arXiv:1808.06013.

*Proc. 26th Int. Symp. Graph Drawing*, Barcelona, 2018.

Springer,*Lecture Notes in Comp. Sci.*11282 (2018), pp. 541–554.

*J. Computational Geometry*10 (1): 257–280, 2019.If you fold a piece of paper flat and unfold it again, the resulting crease pattern forms a planar graph. We prove that a tree can be realized in this way (with its leaves as diverging rays that reach the boundary of the paper) if and only if all internal vertices have odd degree greater than two. On the other hand, for a folding pattern on an infinite sheet of paper with an added vertex at infinity as the endpoint of all its rays, the resulting graph must be 2-vertex-connected and 4-edge-connected.

(Slides)

**Finding maximal sets of laminar 3-separators in planar graphs in linear time**.

D. Eppstein and B. Reed.

arXiv:1810.07825.

*30th ACM-SIAM Symp. on Discrete Algorithms*, San Diego, 2019, pp. 589–605.

Given a 3-vertex-connected planar graph, we find a hierarchical decomposition of the graph by 3-vertex separators, such that each piece of the decomposition is 4-vertex-connected, in linear time. The result has applications to an algorithm of Kawarabayashi, Li, and Reed for finding disjoint paths in nonplanar graphs.

(Slides)

**Minor-closed graph classes with bounded layered pathwidth**.

V. Dujmović, D. Eppstein, G. Joret, P. Morin, and D. R. Wood.

arXiv:1810.08314.

*SIAM J. Discrete Math*34 (3): 1693–1709, 2020.A minor-closed graph family has a functional relation between diameter and path width (bounded local pathwidth) if and only if it excludes an apex-tree. The same graph families are also the ones with bounded layered pathwidth: a simultaneous path decomposition and layering (sequence of subsets of vertices with all edges connecting the same subset or consecutive subsets) so that the intersection of a bag and a layer has constant size.

**Cubic planar graphs that cannot be drawn on few lines**.

D. Eppstein.

arXiv:1903.05256.

*Proc. 35th Int. Symp. on Computational Geometry*, Portland, Oregon, June 2019.

Leibniz International Proceedings in Informatics (LIPIcs) 129, 2019, pp. 32:1–32:15.

*J. Computational Geometry*12 (1): 178–197, 2021.

We construct planar graphs whose straight drawings require a large number of lines (at least the cube root of the number of vertices) to cover all vertices. We also find series-parallel graphs and apex-trees that require a non-constant number of lines.

(Slides)

**Reconfiguring undirected paths**.

E. Demaine, D. Eppstein, A. Hesterberg, K. Jain, A. Lubiw, R. Uehara, and Y. Uno.

arXiv:1905.00518.

*16th Algorithms and Data Structures Symp. (WADS 2019)*, Edmonton, Alberta.

Springer,*Lecture Notes in Comp. Sci.*11646 (2019), pp. 353–365.

A motion that slides an undirected path along its length from one configuration to another in a graph (allowing moves in both directions) can be found in time that is fixed-parameter tractable in the path length. However the problem is PSPACE-complete for paths of unbounded length, even when the host graph has bounded bandwidth.

(Slides)

**Bipartite and series-parallel graphs without planar Lombardi drawings**.

D. Eppstein.

arXiv:1906.04401.

*Proc. 31st Canadian Conference on Computational Geometry*, Edmonton, Canada, 2019, pp. 17–22.

*J. Graph Algorithms & Applications*25 (1): 549–562, 2021.Not every bipartite planar graph has a planar Lombardi drawing. Not every plane series parallel graph has a planar Lombardi drawing with the same embedding. The proof involves the properties of cycles of circular-arc-quadrilaterals all sharing the same two vertices, with equal and sharp vertex angles.

(Slides)

**Graphs in nature**.

D. Eppstein.

Invited talk at Symposium on Geometry Processing, Milan, Italy, July 2019.

Invited talk at Algorithms and Data Structures Symposium, Edmonton, Canada, August 2019.

Invited talk at International Colloquium on Graph Theory and Combinatorics, Montpellier, France, July 2022.

I survey results on characterizing the graphs formed on planar surfaces according to several natural processes: motorcycle graphs, Gilbert tessellations, and the contact graphs of line segments from needle-like crystal growth and crack formation; the graphs of planar soap bubble foams; and graphs representing the fold patterns of crumpled paper.

**C-planarity testing of embedded clustered graphs with bounded dual carving-width**.

G. Da Lozzo, D. Eppstein, M. T. Goodrich, and S. Gupta.

arXiv:1910.02057.

*Proc. 14th International Symposium on Parameterized and Exact Computation (IPEC 2019)*, Munich, Germany, 2019 (best paper award).

Leibniz International Proceedings in Informatics (LIPIcs) 148, 2019, pp. 9:1–9:17.

*Algorithmica*83 (8): 2471–2502, 2021 (special issue for IPEC 2019).We show that finding clustered planar drawings can be done in fixed-parameter-tractable time, depending only on a single width parameter of the input clustered graph.

**Homotopy height, grid-minor height and graph-drawing height**.

T. Biedl, E. Chambers, D. Eppstein, A. de Mesmay, and T. Ophelders.

arXiv:1908.05706.

*Proc. 27th Int. Symp. Graph Drawing*, Prague, Czech Republic, 2019.

Springer,*Lecture Notes in Comp. Sci.*11904 (2019), pp. 468–481.

We lower bound the height of a drawing of a planar graph in an integer grid by a topological invariant, the homotopy height, and show that this invariant is equal to the smallest height of a grid graph in which the given graph is a minor.

**Tracking paths in planar graphs**.

D. Eppstein, M. T. Goodrich, P. Matias, and J. A. Liu.

arXiv:1908.05445.

*Proc. 30th International Symposium on Algorithms and Computation (ISAAC 2019)*, Shanghai, China, 2019.

Leibniz International Proceedings in Informatics (LIPIcs) 149, 2019, pp. 54:1–54:17.A tracking set for a given graph, with designated start and destination vertices, is a set of vertices such that any path from start to destination is determined by the subsequence of its vertices that belong to the tracking set. We show that finding the smallest tracking set is NP-hard but has a constant factor approximation, and can be solved exactly in fixed-parameter-tractable time for graphs of bounded width.

**Simplifying activity-on-edge graphs**.

D. Eppstein, D. Frishberg, and E. Havvaei.

arXiv:2002.01610.

*Proc. 17th Scandinavian Symposium and Workshops on Algorithm Theory (SWAT 2020)*.

Leibniz International Proceedings in Informatics (LIPIcs) 162, 2020, pp. 24:1–24:14.Given a partially ordered set of activities, we find in polynomial time a directed acyclic graph and a mapping from activities to its edges, such that the sequences of activities along paths in the graph are exactly the totally ordered subsets of activities in the input.

**Low-stretch spanning trees of graphs with bounded width**.

G. Borradaile, E. Chambers, D. Eppstein, W. Maxwell, and A. Nayyeri.

arXiv:2004.08375.

*Proc. 17th Scandinavian Symposium and Workshops on Algorithm Theory (SWAT 2020)*.

Leibniz International Proceedings in Informatics (LIPIcs) 162, 2020, pp. 15:1–15:19.We describe a random distribution on the spanning trees of bounded-bandwidth graphs such that each edge has bounded expected stretch, along with several related results for other kinds of graph widths.

**On the treewidth of Hanoi graphs**.

D. Eppstein, D. Frishberg, and W. Maxwell.

arXiv:2005.00179.

*Proc. 10th Int. Conf. Fun with Algorithms (FUN 2021)*.

Leibniz International Proceedings in Informatics (LIPIcs) 157, 2020, pp. 13:1–13:21.

*Theor. Comput. Sci.*906: 1–17, 2022.The

*n*-disc*p*-peg Hanoi graphs have treewidth within a polynomial factor of*n*^{p − 1}.**On the edge crossings of the greedy spanner**.

D. Eppstein and H. Khodabandeh.

arXiv:2002.05854.

*Proc. 37th International Symposium on Computational Geometry (SoCG 2021)*.

Leibniz International Proceedings in Informatics (LIPIcs) 189, 2021, pp. 33:1–33:17.Greedy spanners are graphs formed from sets of geometric points by considering the pairs of points in sorted order by distance and adding an edge whenever a pair cannot be connected by a short path through the previously-added edges. We show that for points in the Euclidean plane, these graphs have linearly many crossings, that the intersection graph of their edges has bounded degeneracy, and that they have separators of square-root size.

**The graphs of stably matchable pairs**.

D. Eppstein.

arXiv:2010.09230.

*47th International Workshop on Graph-Theoretic Concepts in Computer Science (WG 2021)*.

Springer,*Lecture Notes in Comp. Sci.*12911 (2021), pp. 349–360.

If you form a bipartite graph from a stable matching instance, with an edge for each pair that can participate in a stable matching, what graphs can you get? They are matching-covered, but NP-hard to recognize, and their structure is related to the structure of the lattice of stable matchings of the same instance.

(Slides)

**Stack-number is not bounded by queue-number**.

V. Dujmović, D. Eppstein, R. Robert Hickingbotham, P. Morin, and D. R. Wood.

arXiv:2011.04195.

*Combinatorica*42: 151–164, 2022.Stack number is also known as page number or book thickness; it is the minimum number of stacks needed so that you can process the vertices of a graph in some sequence, pushing each edge onto one of the stacks when you process its first endpoint and popping it from the same stack when you process its second endpoint. Queue number is defined in the same way using queues instead of stacks. We show that the strong products of triangular grids and high-degree stars have bounded queue number but unbounded stack number. This result disproves the Blankenship–Oporowski conjecture, according to which subdividing edges of a graph a constant number of times cannot decrease its stack number from non-constant to constant, because subdivisions of the same products also have bounded stack number. It also confirms a conjecture of Bonnet et al on the existence of graphs with bounded sparse twin-width and unbounded stack number.

**A stronger lower bound on parametric minimum spanning trees**.

D. Eppstein.

arXiv:2105.05371.

*17th Algorithms and Data Structures Symp. (WADS 2021)*.

Springer,*Lecture Notes in Comp. Sci.*12808 (2021), pp. 343–356.

*Algorithmica*85: 1738–1753, 2023 (special issue for WADS 2021).

There exist graphs with edges labeled by linear real functions, such that the number of different minimum spanning trees obtained for different choices of the function argument is \(\Omega(m\log n)\).

(Slides)

**Angles of arc-polygons and Lombardi drawings of cacti**.

D. Eppstein, D. Frishberg, and M. Osegueda.

arXiv:2107.03615.

*Proc. 33rd Canadian Conference on Computational Geometry*, 2021, pp. 56–64.

*Comp. Geom. Theory & Applications*112: 101982, 2023 (special issue for CCCG 2021).

We precisely characterize the triples vertex angles that are possible for arc-triangles (curved triangles made from circular arcs), and prove an existence theorem for a large class of sets of angles for arc-polygons. Our characterization allows us to prove that every cactus graph has a planar Lombardi drawing for its natural planar embedding (the embedding in which each cycle is a bounded face), but that there exist other embeddings of cacti that have no Lombardi drawing.

**Parameterized complexity of finding subgraphs with hereditary properties on hereditary graph classes**.

D. Eppstein, E. Havvaei, and S. Gupta.

arXiv:2101.09918.

*Proc. 23rd International Symposium on Fundamentals of Computation Theory*, 2021.

Springer,*Lecture Notes in Comp. Sci.*12867 (2021), pp. 217–229.

We provide a partial classification of the complexity of parameterized graph problems of the form "find a \(k\)-vertex induced subgraph with property \(X\) in a larger subgraph with property \(Y\)", in terms of the existence of large cliques and large independent sets in the graphs with properties \(X\) and \(Y\).

**Distributed construction of lightweight spanners for unit ball graphs**.

D. Eppstein and H. Khodabandeh.

arXiv:2106.15234.

Brief announcement,*34th ACM Symposium on Parallelism in Algorithms and Architectures*, 2022, pp. 57–59.

*Proc. 36th International Symposium on Distributed Computing (DISC 2022)*.

Leibniz International Proceedings in Informatics (LIPIcs) 246, 2022, pp. 21:1–21:23.Metric spaces of bounded doubling dimension have spanners with bounded degree, weight a bounded multiple of the minimum spanning tree weight, and dilation arbitrarily close to one, that can be found efficiently by a distributed algorithm.

**Limitations on realistic hyperbolic graph drawing**.

D. Eppstein.

arXiv:2108.07441.

*Proc. 29th Int. Symp. Graph Drawing*, Tübingen, Germany, 2021.

Springer,*Lecture Notes in Comp. Sci.*12868 (2021), pp. 343–357.

Graphs drawn in the hyperbolic plane can be forced to have features much closer together than unit distance, in the absolute distance scale of the plane. In particular this is true for planar drawings of maximal planar graphs or grid graphs, and for nonplanar drawings of arbitrary graphs.

(Slides)

**Rapid mixing of the hardcore Glauber dynamics and other Markov chains in bounded-treewidth graphs**.

D. Eppstein and D. Frishberg.

arXiv:2111.03898.

*Proc 34th International Symposium on Algorithms and Computation (ISAAC 2023)*.

Leibniz International Proceedings in Informatics (LIPIcs) 283, 2022, pp. 30:1–30:13.A random walk on the independent sets or dominating sets of a graph mixes rapidly for graphs of bounded treewidth, and a random walk on maximal independent sets mixes rapidly for graphs of bounded carving width.

**Three-dimensional graph products with unbounded stack-number**.

D. Eppstein, R. Robert Hickingbotham, L. Merker, S. Norin, M. T. Seweryn, and D. R. Wood.

arXiv:2202.05327.

*Discrete Comput. Geom.*71: 1210–1237, 2024.

The strong product of any three graphs of non-constant size has unbounded book thickness. In the case of strong products of three paths, and more generally of triangulations of \(n\times n\times n\) grid graphs obtained by adding a diagonal to each square of the grid, the book thickness is \(\Theta(n^{1/3})\). This is the first explicit example of a graph family with bounded maximum degree and unbounded book thickness.

**Improved mixing for the convex polygon triangulation flip walk**.

D. Eppstein and D. Frishberg.

arXiv:2207.09972.

*Proc. 50th EATCS International Colloquium on Automata, Languages, and Programming (ICALP 2023)*.

Leibniz International Proceedings in Informatics (LIPIcs) 261, 2023, pp. 56:1–56:17.

The associahedron is a polytope whose vertices represent the triangulations of a convex polygon, and whose edges represent flips connecting one triangulation to another. We show that a random walk on the edges of this polytope rapidly converges to the uniform distribution on triangulations. However, we also show that the associahedron does not have constant expansion.

**Product structure extension of the Alon–Seymour–Thomas theorem**.

M. Distel, V. Dujmović, D. Eppstein, R. Robert Hickingbotham, G. Joret, P. Micek, P. Morin, M. T. Seweryn, and D. R. Wood.

arXiv:2212.08739.

*SIAM J. Discrete Math.*, to appear.

**On the biplanarity of blowups**.

D. Eppstein.

arXiv:2301.09246.

*Proc. 31st Int. Symp. Graph Drawing and Network Visualization*, Palermo, Italy, 2023 (best paper award), to appear.**On the complexity of embedding in graph products**.

T. Biedl, D. Eppstein, and T. Ueckerdt.

arXiv:2303.17028.

*Proc. 35th Canadian Conference on Computational Geometry*, 2023, pp. 77–88.Row treewidth (embedding a graph as a subgraph of a strong product of a path with a low treewidth graph), row pathwidth, and row tree-depth are all NP-hard.

**Lower bounds for non-adaptive shortest path relaxation**.

D. Eppstein.

arXiv:2305.09230.

*Proc. 18th Algorithms and Data Structures Symposium (WADS 2023)*.

Springer,*Lecture Notes in Computer Science*13079 (2023), pp. 416–429.The Bellman–Ford algorithm for single-source shortest paths operates by relaxation steps, in which it checks for a given edge whether the best path it knows to the start of the edge, plus the edge itself, is better than the path it already knows to the end of the edge. We prove that, up to constant factors, Bellman–Ford is optimal among algorithms that use relaxation in an edge ordering that does not depend on the results of earlier relaxation steps.

**Widths of geometric graphs**.

D. Eppstein.

Invited talk, Workshop on Parameterized Algorithms for Geometric Problems, CG Week 2023.

Many computational geometry problems can be solved by transforming them into a graph problem on a geometric graph. When the graph has low width, for some form of graph width, this can often lead to efficient classical or parameterized algorithms. We survey the geometric graphs that always have low width, the geometric graphs that can have high width, and the opportunities for parameterization obtained by studying low-width instances of graphs that sometimes have high width.

**Geometric graphs with unbounded flip-width**.

D. Eppstein and R. McCarty.

arXiv:2306.12611.

*Proc. 35th Canadian Conference on Computational Geometry*, 2023, pp. 197–208.We show that many constructions for dense geometric graphs produce graphs of unbounded flip-width, frustrating the search for natural classes of graphs that have bounded flip-width but unbounded twin-width.

**Quasipolynomiality of the smallest missing induced subgraph**.

D. Eppstein, A. Lincoln, and V. V. Williams.

arXiv:2306.11185.

*J. Graph Algorithms & Applications*27 (5): 329–339, 2023.The smallest graph that is not an induced subgraph of a given graph can be found in time \(n^{O(\log n)}\). The exponent is optimal, up to constant factors, under the exponential time hypothesis.

**Manipulating weights to improve stress-graph drawings of 3-connected planar graphs**.

A. Chiu, D. Eppstein, and M. T. Goodrich.

arXiv:2307.10527.

*Proc. 31st Int. Symp. Graph Drawing and Network Visualization*, Palermo, Italy, 2023, to appear.**The widths of strict outerconfluent graphs**.

D. Eppstein.

arXiv:2308.03967.

*Proc. 31st Int. Symp. Graph Drawing and Network Visualization*, Palermo, Italy, 2023 (poster session), to appear.**Games on game graphs**.

D. Eppstein. AMS Special Session on Serious Recreational Mathematics, Joint Mathematics Meetings, San Francisco, 2024.

This talk surveys graph parameters defined from pursuit-evasion games on graphs, including cop-number, treewidth, and flip-width, and the values of these parameters on graphs derived from games and puzzles.

**Maintaining light spanners via minimal updates**.

D. Eppstein and H. Khodabandeh.

arXiv:2403.03290.

*Proc. 36th Canadian Conference on Computational Geometry*, 2024, to appear.**What is ... treewidth?**.

D. Eppstein.

*Notices of the American Mathematical Society*, to appear.**Drawing planar graphs and 1-planar graphs using cubic Bézier curves with bounded curvature**.

D. Eppstein, M. T. Goodrich, and A. M. Illickan.

*32nd International Symposium on Graph Drawing and Network Visualization*, to appear.

Graph Theory – Publications – David Eppstein – Theory Group – Inf. & Comp. Sci. – UC Irvine

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