This class lays out the vertices of a graph in a hierarchy of vertical levels, with a number of nodes in each level. The number of levels is the depth of the deepest child reachable from some parent at level 0. It implements a layout technique as described by K. Sugiyama, S. Tagawa, and M. Toda. in "Methods for visual understanding of hierarchical systems", IEEE Transactions on Systems, Man and Cybernetics, SMC-11(2):109-125, Feb. 1981.
There have been a few modifications made, however. The crossings function is changed as it was non-linear in time complexity. Furthermore, we don't have any interconnection matrices for each level, instead we just have one big interconnection matrix for the whole graph and a int[][] array which stores the vertices present in each level.
@author Ashraf M. Kibriya (amk14@cs.waikato.ac.nz)
@version $Revision: 7059 $ - 24 Apr 2003 - Initial version (Ashraf M. Kibriya)