Hi, I'm studying MST algorithms in GPU recently.I need BGL implementation as coparison,But I have a problem in using prim_minimum_spanning_tree.hpp.The problem is:when I use large input(e.g. >1M),the result is wrong,all the parent of vertices is "no parent".But when the input(e.g. 1K) is small,the result is noproblem. I haven't found know the reason yet.My complier is gcc 4.1.2,OS is RHEL5. Help would be appreciated. Thanks in advance. Wang wei The complete code is: #include <iostream> #include <boost/graph/adjacency_list.hpp> #include <boost/graph/prim_minimum_spanning_tree.hpp> #include <fstream> #include <string.h> using namespace std; int main() { using namespace boost; typedef adjacency_list < vecS, vecS, undirectedS, property<vertex_distance_t, long>, property < edge_weight_t, int > > Graph; typedef std::pair < long, long >E; //read graph data from file long num_nodes,num_edges,u,v; int w; ifstream infile; infile.open("convertResult.txt"); if(!infile) { cerr<<"error:unable to open file."<<endl; return -1; } infile>>num_nodes>>num_edges; E edges[num_edges]; int weights[num_edges]; for(long i=0;i<num_edges;i++) { infile>>u>>v>>w; edges[i] = make_pair(u,v); weights[i] = w; } //construct input parameters Graph g(edges, edges + sizeof(edges) / sizeof(E), weights, num_nodes); property_map<Graph, edge_weight_t>::type weightmap = get(edge_weight, g); std::vector < graph_traits < Graph >::vertex_descriptor > p(num_vertices(g)); //call the BGL PRIM prim_minimum_spanning_tree(g, &p[0]); //output the result ofstream outfile; outfile.open("primResult.txt"); for (std::size_t i = 0; i != p.size(); ++i) if (p[i] != i) outfile<< "parent[" << i << "] = " << p[i] << std::endl; else outfile<< "parent[" << i << "] = no parent" << std::endl; return EXIT_SUCCESS; }