send column 1 of a matrix on process 0 to row 1 * on process 1.

/* send_col_to_row.c -- send column 1 of a matrix on process 0 to row 1
* on process 1.
*
* Input: none
* Output: The row received by process 1.
*
* Note: This program should only be run with 2 processes
*
* See Chap 6., pp. 98 & ff in PPMPI
*/
#include
#include "mpi.h"

main(int argc, char* argv[]) {
int p;
int my_rank;
float A[10][10];
MPI_Status status;
MPI_Datatype column_mpi_t;
int i, j;

MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);

MPI_Type_vector(10, 1, 10, MPI_FLOAT, &column_mpi_t);
MPI_Type_commit(&column_mpi_t);

if (my_rank == 0) {
for (i = 0; i < 10; i++)
for (j = 0; j < 10; j++)
A[i][j] = (float) i;
MPI_Send(&(A[0][0]), 1, column_mpi_t, 1, 0,
MPI_COMM_WORLD);
} else { /* my_rank = 1 */
for (i = 0; i < 10; i++)
for (j = 0; j < 10; j++)
A[i][j] = 0.0;
MPI_Recv(&(A[0][0]), 10, MPI_FLOAT, 0, 0,
MPI_COMM_WORLD, &status);
for (j = 0; j < 10; j++)
printf("%3.1f ", A[0][j]);
printf("\n");
}

MPI_Finalize();
} /* main */