Matrix Multiplication using MPI with C

Here I'll give you a code for matrix multiplication using Message passing interface (MPI). If you are dealing with parallel computing MPI will take major role. Before run the MPI codes you will need to have MPI environment. In my case I am using university cluster.

Here is code

 /**********************************************************************  
  * MPI-based matrix multiplication AxB=C   
  *********************************************************************/  
 #include <stdio.h>  
 #include "mpi.h"  
 #define N 500    /* number of rows and columns in matrix */  
 MPI_Status status;  
 double a[N][N],b[N][N],c[N][N];       
 main(int argc, char **argv)   
 {  
  int numtasks,taskid,numworkers,source,dest,rows,offset,i,j,k,remainPart,originalRows;  
  struct timeval start, stop;  
  MPI_Init(&argc, &argv);  
  MPI_Comm_rank(MPI_COMM_WORLD, &taskid);  
  MPI_Comm_size(MPI_COMM_WORLD, &numtasks);  
  numworkers = numtasks-1;  
  /*---------------------------- master ----------------------------*/  
  if (taskid == 0) {  
   for (i=0; i<N; i++) {  
    for (j=0; j<N; j++) {    
     a[i][j]= 1.0;  
     b[i][j]= 2.0;  
    }  
   }  
   gettimeofday(&start, 0);  
   /* send matrix data to the worker tasks */  
   rows = N/numworkers;  
   offset = 0;  
   remainPart = N%numworkers;  
   for (dest=1; dest<=numworkers; dest++)   
   {          
    if (remainPart > 0)  
    {      
      originalRows = rows;  
      ++rows;  
      remainPart--;  
      MPI_Send(&offset, 1, MPI_INT, dest, 1, MPI_COMM_WORLD);  
      MPI_Send(&rows, 1, MPI_INT, dest, 1, MPI_COMM_WORLD);  
      MPI_Send(&a[offset][0], rows*N, MPI_DOUBLE,dest,1, MPI_COMM_WORLD);  
      MPI_Send(&b, N*N, MPI_DOUBLE, dest, 1, MPI_COMM_WORLD);  
      offset = offset + rows;   
      rows = originalRows;  
    }  
    else  
    {      
        MPI_Send(&offset, 1, MPI_INT, dest, 1, MPI_COMM_WORLD);  
        MPI_Send(&rows, 1, MPI_INT, dest, 1, MPI_COMM_WORLD);  
        MPI_Send(&a[offset][0], rows*N, MPI_DOUBLE,dest,1, MPI_COMM_WORLD);  
        MPI_Send(&b, N*N, MPI_DOUBLE, dest, 1, MPI_COMM_WORLD);  
        offset = offset + rows;  
    }  
   }  
   /* wait for results from all worker tasks */  
   for (i=1; i<=numworkers; i++)      
   {              
    source = i;  
    MPI_Recv(&offset, 1, MPI_INT, source, 2, MPI_COMM_WORLD, &status);  
    MPI_Recv(&rows, 1, MPI_INT, source, 2, MPI_COMM_WORLD, &status);  
    MPI_Recv(&c[offset][0], rows*N, MPI_DOUBLE, source, 2, MPI_COMM_WORLD, &status);  
   }  
   gettimeofday(&stop, 0);  
   /* printf("Here is the result matrix:\n");  
   for (i=0; i<N; i++) {   
    for (j=0; j<N; j++)   
     printf("%6.2f  ", c[i][j]);  
    printf ("\n");  
   }  
  */  
   fprintf(stdout,"Time = %.6f\n\n",  
      (stop.tv_sec+stop.tv_usec*1e-6)-(start.tv_sec+start.tv_usec*1e-6));  
  }   
  /*---------------------------- worker----------------------------*/  
  if (taskid > 0) {  
   source = 0;  
   MPI_Recv(&offset, 1, MPI_INT, source, 1, MPI_COMM_WORLD, &status);  
   MPI_Recv(&rows, 1, MPI_INT, source, 1, MPI_COMM_WORLD, &status);  
   MPI_Recv(&a, rows*N, MPI_DOUBLE, source, 1, MPI_COMM_WORLD, &status);  
   MPI_Recv(&b, N*N, MPI_DOUBLE, source, 1, MPI_COMM_WORLD, &status);  
   /* Matrix multiplication */  
   for (k=0; k<N; k++)  
    for (i=0; i<rows; i++) {  
     c[i][k] = 0.0;  
     for (j=0; j<N; j++)  
      c[i][k] = c[i][k] + a[i][j] * b[j][k];  
    }  
   MPI_Send(&offset, 1, MPI_INT, 0, 2, MPI_COMM_WORLD);  
   MPI_Send(&rows, 1, MPI_INT, 0, 2, MPI_COMM_WORLD);  
   MPI_Send(&c, rows*N, MPI_DOUBLE, 0, 2, MPI_COMM_WORLD);  
  }   
  MPI_Finalize();  
 }   

How to compile

How to run

Special Thanks for Mr. K.P.M.K. Silva - BSc (Col), MSc(York) (Lecturer)