mpi_mm.c

/******************************************************************************
* FILE: mpi_mm.c
* DESCRIPTION:  
*   MPI Matrix Multiply - C Version
*   In this code, the master task distributes a matrix multiply
*   operation to numtasks-1 worker tasks.
*   NOTE:  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: Blaise Barney. Adapted from Ros Leibensperger, Cornell Theory
*   Center. Converted to MPI: George L. Gusciora, MHPCC (1/95)
* LAST REVISED: 04/13/05
******************************************************************************/
#include "mpi.h"
#include <stdio.h>
#include <stdlib.h>

#define NRA 1000                 /* number of rows in matrix A */
#define NCA 5000                 /* number of columns in matrix A */
#define NCB 1200               /* 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 */

double *a = NULL;           /* matrix A to be multiplied */
double *b = NULL;           /* matrix B to be multiplied */
double *c = NULL;           /* result matrix C */

inline double* getA(size_t i, size_t j)
{
  return &a[i * NCA + j];
}

inline double* getB(size_t i, size_t j)
{
  return &b[i * NCB + j];
}

inline double* getC(size_t i, size_t j)
{
  return &c[i * NCB + j];
}

int 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 */
	mtype,                 /* message type */
	rows,                  /* rows of matrix A sent to each worker */
	averow, extra, offset, /* used to determine rows sent to each worker */
	i, j, k, rc;           /* misc */

MPI_Status status;

MPI_Init(&argc,&argv);
MPI_Comm_rank(MPI_COMM_WORLD,&taskid);
MPI_Comm_size(MPI_COMM_WORLD,&numtasks);
if (numtasks < 2 ) {
	//printf("Need at least two MPI tasks. Quitting...\n");
	MPI_Abort(MPI_COMM_WORLD, rc);
	exit(1);
}
	numworkers = numtasks-1;
	a = calloc(NRA * NCA, sizeof(double));
	b = calloc(NCA * NCB, sizeof(double));
	c = calloc(NRA * NCB, sizeof(double));

/**************************** master task ************************************/
   if (taskid == MASTER)
   {
      printf("mpi_mm has started with %d tasks.\n",numtasks);
      printf("Initializing arrays...\n");
      for (i=0; i<NRA; i++)
         for (j=0; j<NCA; j++)
            *getA(i,j) = i+j;
      for (i=0; i<NCA; i++)
         for (j=0; j<NCB; j++)
            *getB(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 offset=%d\n",rows,dest,offset);
         MPI_Send(&offset, 1, MPI_INT, dest, mtype, MPI_COMM_WORLD);
         MPI_Send(&rows, 1, MPI_INT, dest, mtype, MPI_COMM_WORLD);
         MPI_Send(getA(offset, 0), rows*NCA, MPI_DOUBLE, dest, mtype,
                   MPI_COMM_WORLD);
         MPI_Send(b, NCA*NCB, MPI_DOUBLE, dest, mtype, MPI_COMM_WORLD);
         offset = offset + rows;
      }

      /* Receive results from 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);
         MPI_Recv(getC(offset,0), rows*NCB, MPI_DOUBLE, source, mtype, 
                  MPI_COMM_WORLD, &status);
         //printf("Received results from task %d\n",source);
      }
   }


/**************************** worker task ************************************/
   if (taskid > MASTER)
   {
      mtype = FROM_MASTER;
      MPI_Recv(&offset, 1, MPI_INT, MASTER, mtype, MPI_COMM_WORLD, &status);
      MPI_Recv(&rows, 1, MPI_INT, MASTER, mtype, MPI_COMM_WORLD, &status);
      MPI_Recv(a, rows*NCA, MPI_DOUBLE, MASTER, mtype, MPI_COMM_WORLD, &status);
      MPI_Recv(b, NCA*NCB, MPI_DOUBLE, MASTER, mtype, MPI_COMM_WORLD, &status);

      for (k=0; k<NCB; k++)
         for (i=0; i<rows; i++)
         {
            *getC(i,k) = 0.0;
            for (j=0; j<NCA; j++)
               *getC(i,k) = (*getC(i,k)) + (*getA(i,j)) * (*getB(j,k));
         }
      mtype = FROM_WORKER;
      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);
   }
   MPI_Finalize();
}