send the upper triangle of a matrix from process 0 * to process 1

/* send_triangle.c -- send the upper triangle of a matrix from process 0
* to process 1
*
* Input: None
* Output: The matrix received by process 1
*
* Note: This program should only be run with 2 processes.
*
* See Chap 6, p. 98, in PPMPI.
*/
#include
#include "mpi.h"

#define n 10

main(int argc, char* argv[]) {
int p;
int my_rank;
float A[n][n]; /* Complete Matrix */
float T[n][n]; /* Upper Triangle */
int displacements[n];
int block_lengths[n];
MPI_Datatype index_mpi_t;
int i, j;
MPI_Status status;

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

for (i = 0; i < n; i++) {
block_lengths[i] = n-i;
displacements[i] = (n+1)*i;
}
MPI_Type_indexed(n, block_lengths, displacements,
MPI_FLOAT, &index_mpi_t);
MPI_Type_commit(&index_mpi_t);

if (my_rank == 0) {
for (i = 0; i < n; i++)
for (j = 0; j < n; j++)
A[i][j] = (float) i + j;
MPI_Send(A, 1, index_mpi_t, 1, 0, MPI_COMM_WORLD);
} else {/* my_rank == 1 */
for (i = 0; i < n; i++)
for (j = 0; j < n; j++)
T[i][j] = 0.0;
MPI_Recv(T, 1, index_mpi_t, 0, 0, MPI_COMM_WORLD, &status);
for (i = 0; i < n; i++) {
for (j = 0; j < n; j++)
printf("%4.1f ", T[i][j]);
printf("\n");
}
}

MPI_Finalize();
} /* main */