void update(float *coord)
Convert the given Cartesian x, y, z coordinates in coord to internal coordinates in-place. On input, coord[0] should contain the x coordinate, coord[1] the y coordinate and coord[2] the z coordinate of an atom position or location. Upon return coord[0] contains the distance to the location, coord[1] contains the angle to the two previous locations and coord[2] the signed torsion to the previous three locations.