pack a row of a sparse matrix and send from process 0 * to process 1. Process 1 allocates required storage after partially * unpacking.

/* sparse_row.c -- pack a row of a sparse matrix and send from process 0
* to process 1. Process 1 allocates required storage after partially
* unpacking.
*
* Input: none
* Output: the row received by process 1.
*
* Notes:
* 1. This program should only be run with 2 processes.
* 2. Only the row of the matrix is created on both processes.
*
* See Chap. 6, pp. 104 & ff in PPMPI
*/
#include
#include
#include "mpi.h"

#define HUGE 100

main(int argc, char* argv[]) {
int p;
int my_rank;
float* entries;
int* column_subscripts;
int nonzeroes;
int position;
int row_number;
char buffer[HUGE]; /* HUGE is a predefined constant */
MPI_Status status;
int i;

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

if (my_rank == 0) {
/* Get the number of nonzeros in the row. */
/* Allocate storage for the row. */
/* Initialize entries and column_subscripts */
nonzeroes = 10;
entries = (float*) malloc(nonzeroes*sizeof(float));
column_subscripts = (int*) malloc(nonzeroes*sizeof(int));
for (i = 0; i < nonzeroes; i++) {
entries[i] = (float) 2*i;
column_subscripts[i] = 3*i;
}

/* Now pack the data and send */
position = 0;
MPI_Pack(&nonzeroes, 1, MPI_INT, buffer, HUGE,
&position, MPI_COMM_WORLD);
MPI_Pack(&row_number, 1, MPI_INT, buffer, HUGE,
&position, MPI_COMM_WORLD);
MPI_Pack(entries, nonzeroes, MPI_FLOAT, buffer,
HUGE, &position, MPI_COMM_WORLD);
MPI_Pack(column_subscripts, nonzeroes, MPI_INT,
buffer, HUGE, &position, MPI_COMM_WORLD);
MPI_Send(buffer, position, MPI_PACKED, 1, 0,
MPI_COMM_WORLD);
} else { /* my_rank == 1 */
MPI_Recv(buffer, HUGE, MPI_PACKED, 0, 0,
MPI_COMM_WORLD, &status);
position = 0;
MPI_Unpack(buffer, HUGE, &position, &nonzeroes,
1, MPI_INT, MPI_COMM_WORLD);
MPI_Unpack(buffer, HUGE, &position, &row_number,
1, MPI_INT, MPI_COMM_WORLD);
/* Allocate storage for entries and column_subscripts */
entries = (float *) malloc(nonzeroes*sizeof(float));
column_subscripts = (int *) malloc(nonzeroes*sizeof(int));
MPI_Unpack(buffer,HUGE, &position, entries,
nonzeroes, MPI_FLOAT, MPI_COMM_WORLD);
MPI_Unpack(buffer, HUGE, &position, column_subscripts,
nonzeroes, MPI_INT, MPI_COMM_WORLD);
for (i = 0; i < nonzeroes; i++)
printf("%4.1f %2d\n", entries[i], column_subscripts[i]);
}

MPI_Finalize();
} /* main */