The rank of the Dehn invariant of an orthogonal polygon equals the minimum number of rectangles into which it can be transformed by axis-parallel cuts, translation, and gluing. This allows the minimum number of rectangles to be calculated in polynomial time.
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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.
Non-collinear point sets with integer distances must be finite, for strictly convex distance functions on the plane, for two-dimensional complete Riemannian manifolds of bounded genus, and for geodesic distance on convex surfaces in 3d.
We survey graph treewidth at a high level. The focus is on applications of treewidth to various areas of mathematics.
We describe the experience of editing mathematics articles on Wikipedia, with the aim of providing helpful advice for new editors and encouraging mathematicians to become Wikipedia editors.
An algorithm that uses Boolean primitive operations, like comparisons, that may be erroneous with some small independent probability per call, may be made to run correctly with high probability by repeating each primitive enough times to be sure its majority result is correct, but this incurs a logarithmic time penalty. Prior work avoids this penalty for sorting; we extend this speedup to algorithms in computational geometry that can be formulated using path search in DAGs. Applications of our "path-guided pushdown random walk" technique include point location, plane sweep, convex hulls, and Delaunay triangulation.
We provide fast parallel and bit-parallel data structures for string search in a dynamic set of strings, with few bits of metadata per node.
My 1994 paper "On the number of minimal 1-Steiner trees" with Aronov and Bern, in some preliminary manuscript versions, included a bound of \(O(m^{\lceil d/2\rceil}n^{\lfloor d/2\rfloor})\) on the complexity of an arrangement of \(m\) convex polytopes given as intersections of a total of \(n\) halfspaces, interpolating between the upper bound theorem for polytopes and the complexity of hyperplane arrangements. However, the manuscript and the proof were lost. This paper re-proves the result, with better care for the degenerate cases.
In graphs of bounded bandwidth, the number of vertices per level of a breadth-first search tree is at most polylogarithmic, with the exponent of the polylogarithm both upper and lower bounded by functions of the bandwidth. This has applications to the Cuthull-McKee heuristic and reverse Cuthull-McKee heuristic in sparse numerical algebra, to reconstructing an unknown graph by shortest distance queries, and to drawing graphs as arc diagrams of small height.
For given elements and a quality function of an element in a subset, monotonically non-increasing with respect to removals of other elements, we can find the max-min-quality subset by a decremental greedy algorithm that repeatedly removes low-quality subsets. We apply this method to find the max-min-angle polygon for points in the plane, the max-min-weight cycle in a directed graph, and several generalizations of both problems.
We define a notion of structural entropy of point sets under which a set has low entropy when it can be covered by few disjoint triangles that are either entirely under the hull of the input or presorted, and show that we can find the hull in time sensitive to this entropy. Generalizations of the same technique apply to geometric maxima, lower envelopes, and visibility polygons.
For each smooth convex curve \(C\), and each planar graph \(G\), there exists a straight-line drawing of \(G\) all of whose faces are crossed by \(C\). This result serves as a counterexample to an argument that universal point sets for planar graph drawing cannot be covered by few convex polygons.
Years – Publications – David Eppstein – Theory Group – Inf. & Comp. Sci. – UC Irvine
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