Hello everyone, I use mpich2 on a small cluster of 3 nodes and each node has Ubuntu 12.04 installed. I use this cluster to do the following. 1. *Master *node send some matrices to the 2 *workers* 2. Workers perform some calculations and send the resulted matrices back to the master. 3. Master perform some final calculations. code snippet: //n*n is the matrix size //master(taskid=0) MPI_Send(ha11, n / 2 * n / 2, MPI_DOUBLE, 1, 1, MPI_COMM_WORLD); //to worker 1 MPI_Send(ha11, n / 2 * n / 2, MPI_DOUBLE, 2, 1, MPI_COMM_WORLD); //to worker 2 MPI_Recv(hM1, n / 2 * n / 2, MPI_DOUBLE, 1, 2, MPI_COMM_WORLD,&status); //from worker 1 MPI_Recv(hM2, n / 2 * n / 2, MPI_DOUBLE, 2, 2, MPI_COMM_WORLD,&status);//from worker 2 //final calculations using hM1,hM2 //worker 1 (taskid=1) MPI_Recv(ha11, n / 2 * n / 2, MPI_DOUBLE, 0, 1, MPI_COMM_WORLD,&status); //does some calculations MPI_Send(hM1, n / 2 * n / 2, MPI_DOUBLE, 0, 2, MPI_COMM_WORLD); //sends back //worker 2(taskid=2) MPI_Recv(ha11, n / 2 * n / 2, MPI_DOUBLE, 0, 1, MPI_COMM_WORLD,&status); //does some calculations MPI_Send(hM2, n / 2 * n / 2, MPI_DOUBLE, 0, 2, MPI_COMM_WORLD); //sends back This worked fine at first, for n=128 to n=2048. But after I pushed 'n' beyond 2048 I got a segmentation fault from the worker 1. Since then, code works fine for the small n values. But whenever I set the value n=128 or greater, worker 1 is getting delayed indefinitely while the rest of the nodes works fine. What could be the reason for this? And how can I resolve this? If I have done any mistakes please point out. Thanks in advance. -- Regards, *H.K. Madhawa Bandara*