I am trying to create undirected weighted graph on two mpi-processes. I use add_edge function to add edges (master (pid=0) process is responsible for this). For small graphs everything is ok. But when I create larger graphs (for instance, number of vertices is 2^20 and number of edges is 2^28) the program hangs supposedly in add_edge.  For mpirun -np 1 there is no such problem.

What can cause this issue? Thanks for any help!

Best, 

   Alex