Accodring to <http://www.boost.org/libs/graph/doc/transpose_graph.html> the graph that will hold the transposition is supposed to have no edges in it and to have the same number of vertices as the input graph. However, looking through the source code in <boost/graph/copy.hpp>, which the algorithm uses, I see as many vertices being added to the output graph as there are in the input graph. Does this mean that the output graph is actually supposed to have no vertices to begin with? In the attached program, if the #if condition is set to 1, the program does as the documentation currently suggests, but the output is wrong. With the #if condition left at 0, the program gives the correct output. What's the verdict? Cromwell Enage __________________________________ Do you Yahoo!? Yahoo! Mail SpamGuard - Read only the mail you want. http://antispam.yahoo.com/tools