Hi I am a very fresh user of Boost library. While I was searching the internet for a bandwidth optimization algorithm, I found Boost Graph Library. The library supports an RCM algorithm (cuthill_mckee_ordering) and I have checked the example given at this address: http://www.boost.org/libs/graph/example/cuthill_mckee_ordering.cpp It seems like the used vertex numbers given in this example is sequential and starts form 0: vertex list: 0, 1, 2, 3, 4, 5, 6, 7,8, 9 and a edge list is constructed from these vertex numbers. Do I have to define such a sequential order and always start from 0? What if I define vertex numbers such as : 1, 6, 9, 10, 11, 13, 21, 25, 26, 30, and define a valid edge like: ( 1,10), (1,13), (6,21), (6,30), (6,11), (6,9), (10,13), (10,26), (10,9), (13,21), (21,25), (9,11), (13,35) The above vertex list is a relabed list of the one given in the example code and I defined the same edge (connectivity) list. In fact, I tried it but the returned ordered list is not valid. Unless I use the vertex numbers starting from 0 and goes up to 9 like given on the example, the returned ordered is wrong. I really appreciate your comments and helps on this thanks bulent