Parallel Matrix Multiplication in MPI

/******************************************************************************
* FILE: mm.c
* DESCRIPTION:
* In this template code, the master task distributes a matrix multiply
* operation to numtasks-1 worker tasks.
* NOTE1: C and Fortran versions of this code differ because of the way
* arrays are stored/passed. C arrays are row-major order but Fortran
* arrays are column-major order.
* AUTHOR for MPL version: Ros Leibensperger / Blaise Barney
* LAST MPL REVISED: 09/14/93 for latest API changes. Blaise Barney
* CONVERTED TO MPI: 11/12/94 by Xianneng Shen
******************************************************************************/

#include
#include "mpi.h"
#define NRA 62 /* number of rows in matrix A */
#define NCA 15 /* number of columns in matrix A */
#define NCB 7 /* number of columns in matrix B */
#define MASTER 0 /* taskid of first task */
#define FROM_MASTER 1 /* setting a message type */
#define FROM_WORKER 2 /* setting a message type */

MPI_Status status;
main(int argc, char **argv)
{
int numtasks, /* number of tasks in partition */
taskid, /* a task identifier */
numworkers, /* number of worker tasks */
source, /* task id of message source */
dest, /* task id of message destination */
nbytes, /* number of bytes in message */
mtype, /* message type */
intsize, /* size of an integer in bytes */
dbsize, /* size of a double float in bytes */
rows, /* rows of matrix A sent to each worker */
averow, extra, offset, /* used to determine rows sent to each worker */
i, j, k, /* misc */
count;
double a[NRA][NCA], /* matrix A to be multiplied */
b[NCA][NCB], /* matrix B to be multiplied */
c[NRA][NCB]; /* result matrix C */

intsize = sizeof(int);
dbsize = sizeof(double);

MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &taskid);
MPI_Comm_size(MPI_COMM_WORLD, &numtasks);
numworkers = numtasks-1;

/**************************** master task ************************************/
if (taskid == MASTER) {
printf("Number of worker tasks = %d\n",numworkers);
for (i=0; i for (j=0; j a[i][j]= i+j;
for (i=0; i for (j=0; j b[i][j]= i*j;

/* send matrix data to the worker tasks */
averow = NRA/numworkers;
extra = NRA%numworkers;
offset = 0;
mtype = FROM_MASTER;
for (dest=1; dest<=numworkers; dest++) {
rows = (dest <= extra) ? averow+1 : averow;
printf(" sending %d rows to task %d\n",rows,dest);
MPI_Send(&offset, 1, MPI_INT, dest, mtype, MPI_COMM_WORLD);
MPI_Send(&rows, 1, MPI_INT, dest, mtype, MPI_COMM_WORLD);
count = rows*NCA;
MPI_Send(&a[offset][0], count, MPI_DOUBLE, dest, mtype, MPI_COMM_WORLD);
count = NCA*NCB;
MPI_Send(&b, count, MPI_DOUBLE, dest, mtype, MPI_COMM_WORLD);

offset = offset + rows;
}

/* wait for results from all worker tasks */
mtype = FROM_WORKER;
for (i=1; i<=numworkers; i++) {
source = i;
MPI_Recv(&offset, 1, MPI_INT, source, mtype, MPI_COMM_WORLD, &status);
MPI_Recv(&rows, 1, MPI_INT, source, mtype, MPI_COMM_WORLD, &status);
count = rows*NCB;
MPI_Recv(&c[offset][0], count, MPI_DOUBLE, source, mtype, MPI_COMM_WORLD,
&status);

}

/* print results */
printf("Here is the result matrix\n");
for (i=0; i printf("\n");
for (j=0; j printf("%6.2f ", c[i][j]);
}
printf ("\n");

} /* end of master section */



/**************************** worker task ************************************/
if (taskid > MASTER) {
mtype = FROM_MASTER;
source = MASTER;
printf ("Master =%d, mtype=%d\n", source, mtype);
MPI_Recv(&offset, 1, MPI_INT, source, mtype, MPI_COMM_WORLD, &status);
printf ("offset =%d\n", offset);
MPI_Recv(&rows, 1, MPI_INT, source, mtype, MPI_COMM_WORLD, &status);
printf ("row =%d\n", rows);
count = rows*NCA;
MPI_Recv(&a, count, MPI_DOUBLE, source, mtype, MPI_COMM_WORLD, &status);
printf ("a[0][0] =%e\n", a[0][0]);
count = NCA*NCB;
MPI_Recv(&b, count, MPI_DOUBLE, source, mtype, MPI_COMM_WORLD, &status);
printf ("b=\n");
for (k=0; k for (i=0; i c[i][k] = 0.0;
for (j=0; j c[i][k] = c[i][k] + a[i][j] * b[j][k];
}

mtype = FROM_WORKER;
printf ("after computer\n");
MPI_Send(&offset, 1, MPI_INT, MASTER, mtype, MPI_COMM_WORLD);
MPI_Send(&rows, 1, MPI_INT, MASTER, mtype, MPI_COMM_WORLD);
MPI_Send(&c, rows*NCB, MPI_DOUBLE, MASTER, mtype, MPI_COMM_WORLD);
printf ("after send\n");

} /* end of worker */
MPI_Finalize();
} /* of main */