Hi, I try to familiar with mpi self defined type api, and I directly run a very simple code from LLNL webpage: //----------------------------------------------------------------------------------------------- #include "mpi.h" #include <stdio.h> #define SIZE 4 int main(argc,argv) int argc; char *argv[]; { int numtasks, rank, source=0, dest, tag=1, i; float a[SIZE][SIZE] = {1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0}; float b[SIZE]; MPI_Status stat;MPI_Datatype columntype; MPI_Init(&argc,&argv);MPI_Comm_rank(MPI_COMM_WORLD, &rank);MPI_Comm_size(MPI_COMM_WORLD, &numtasks); MPI_Type_vector(SIZE, 1, SIZE, MPI_FLOAT, &columntype);MPI_Type_commit(&columntype); if (numtasks == SIZE) { if (rank == 0) { for (i=0; i<numtasks; i++) MPI_Send(&a[0][i], 1, columntype, i, tag, MPI_COMM_WORLD); } MPI_Recv(b, SIZE, MPI_FLOAT, source, tag, MPI_COMM_WORLD, &stat); printf("rank= %d b= %3.1f %3.1f %3.1f %3.1f\n", rank,b[0],b[1],b[2],b[3]); } else printf("Must specify %d processors. Terminating.\n",SIZE); MPI_Type_free(&columntype);MPI_Finalize(); } //----------------------------------------------------------------------------------------------- However, it doesn't work. the program just suspend there. I figure out the problem is at line MPI_Send, and MPI_Recv. the MPI_Send just send it to itself. but I don't know why it doesn't work. Is it caused by dead lock? why? Thank you very much! -- Best Regards, Sufeng Niu ECASP lab, ECE department, Illinois Institute of Technology Tel: 312-731-7219