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112 lines
3.7 KiB
112 lines
3.7 KiB
#include <stdio.h>
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#include <stdlib.h>
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#include "mpi.h"
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#define MAXPROC 8 /* Max number of procsses */
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#define NAMELEN 80 /* Max length of machine name */
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#define LENGTH 8 /* Size of matrix is LENGTH * LENGTH */
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main(int argc, char* argv[]) {
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int i, j, np, me, count;
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const int nametag = 42; /* Tag value for sending name */
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const int datatag = 43; /* Tag value for sending data */
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const int root = 0; /* Root process in scatter */
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MPI_Status status; /* Status object for receive */
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char myname[NAMELEN]; /* Local host name string */
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char hostname[MAXPROC][NAMELEN]; /* Received host names */
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int x[LENGTH][LENGTH]; /* Send buffer */
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int y[LENGTH]; /* Receive buffer */
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int *sendcount, *displs; /* Arrays for sendcounts and displacements */
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MPI_Init(&argc, &argv); /* Initialize MPI */
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MPI_Comm_size(MPI_COMM_WORLD, &np); /* Get nr of processes */
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MPI_Comm_rank(MPI_COMM_WORLD, &me); /* Get own identifier */
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gethostname(&myname, NAMELEN); /* Get host name */
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/* Check that we have one process for each row in the matrix */
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if (np != LENGTH) {
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if (me == 0) {
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printf("You have to use %d processes\n", LENGTH);
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}
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MPI_Finalize();
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exit(0);
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}
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/* Allocate memory for the sendcount and displacements arrays */
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sendcount = (int *)malloc(LENGTH*sizeof(int));
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displs = (int *)malloc(LENGTH*sizeof(int));
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/* Initialize sendcount and displacements arrays */
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for (i=0; i<LENGTH; i++) {
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sendcount[i] = i+1;
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displs[i] = i*LENGTH;
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}
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if (me == 0) { /* Process 0 does this */
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/* Initialize the matrix x with values 0 .. LENGTH*LENGTH-1 */
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for (i=0; i<LENGTH; i++) {
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for (j=0; j<LENGTH; j++) {
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x[i][j] = i*LENGTH+j;
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}
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}
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/* Print out the matrix before it is distributed */
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printf("The matrix is\n");
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for (i=0; i<LENGTH; i++) {
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for (j=0; j<LENGTH; j++) {
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printf("%4d ", x[i][j]);
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}
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printf("\n");
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}
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printf("\nProcess %d on host %s is scatteringing the lower triangular part of the matrix x to all %d processes\n\n", me, myname, np);
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/* Scatter the lower triangular part of array x to all proceses, place it in y */
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MPI_Scatterv(&x, sendcount, displs, MPI_INT, &y, LENGTH, MPI_INT, root, MPI_COMM_WORLD);
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/* Process zero prints out own portion of the scattered array */
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for (i=0; i<sendcount[me]; i++) {
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printf("%4d", y[i]);
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}
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printf(" ");
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printf(" from process %d on host %s\n", me, myname);
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/* Receive messages with hostname and the scattered data */
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/* from all other processes */
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for (i=1; i<np; i++) {
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MPI_Recv (&hostname[i], NAMELEN, MPI_CHAR, i, nametag, MPI_COMM_WORLD, \
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&status);
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MPI_Recv (&y, LENGTH, MPI_INT, i, datatag, MPI_COMM_WORLD, &status);
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MPI_Get_count(&status, MPI_INT, &count); /* Get nr of elements in message */
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/* Print out the elements we received from this process */
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for (j=0; j<count; j++) {
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printf("%4d", y[j]);
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}
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for (j=0; j<LENGTH-count; j++) { /* Format output to look like a matrix */
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printf(" ");
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}
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printf(" from process %d on host %s\n", i, hostname[i]);
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}
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printf("Ready\n");
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} else { /* all other processes do this */
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/* Receive the scattered matrix from process 0, place it in array y */
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MPI_Scatterv(&x, sendcount, displs, MPI_INT, &y, LENGTH, MPI_INT, root, MPI_COMM_WORLD);
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/* Send own name back to process 0 */
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MPI_Send (&myname, NAMELEN, MPI_CHAR, 0, nametag, MPI_COMM_WORLD);
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/* Send the received array back to process 0 */
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MPI_Send (&y, sendcount[me], MPI_INT, 0, datatag, MPI_COMM_WORLD);
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}
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MPI_Finalize();
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}
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