Standard Matrix Multiplication

matrix_mul.c

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>

void Multiply(int n, double** a, double** b, double** c)
{
  int i=0;
  int j=0;
  int k=0;
  for(i = 0; i < n; i++)
    for( j = 0; j < n; j++)
      for( k = 0; k < n; k++)
        c[i][j] +=  a[i][k] * b[k][j];
}

int main(void)
{
  int n;
  double** A;
  double** B;
  double** C;
  int numreps = 5;
  int i=0;
  int j=0;
  struct timeval tv1, tv2;
  struct timezone tz;  
  double elapsed;
  printf ("Please enter matrix dimension n : ");
  scanf("%d", &n);
  
  // allocate memory for the matrices

  ///////////////////// Matrix A //////////////////////////

  A =(double **)malloc(n*sizeof(double *));
  A[0] = (double *)malloc(n*n*sizeof(double));
  if(!A)
  {
    printf("memory failed \n");
    exit(1);
  }
  for(i=1; i<n; i++)
  {
    A[i] = A[0]+i*n;
    if (!A[i])
    {
      printf("memory failed \n");
      exit(1);
    }
  }

  ///////////////////// Matrix B //////////////////////////

  B =(double **)malloc(n*sizeof(double *));
  B[0] = (double *)malloc(n*n*sizeof(double));
  if(!B)
  {
    printf("memory failed \n");
    exit(1);
  }
  for(i=1; i<n; i++)
  {
    B[i] = B[0]+i*n;
    if (!B[i])
    {
      printf("memory failed \n");
      exit(1);
    }
  }

  ///////////////////// Matrix C //////////////////////////
  
  C =(double **)malloc(n*sizeof(double *));
  C[0] = (double *)malloc(n*n*sizeof(double));
  if(!C)
  {
    printf("memory failed \n");
    exit(1);
  }
  for(i=1; i<n; i++)
  {
    C[i] = C[0]+i*n;
    if (!C[i])
    {
      printf("memory failed \n");
      exit(1);
    }
  }

  // initialize the matrices
  
  for(i=0; i<n; i++)
  {
    for(j=0; j<n; j++)
    {
      A[i][j] = 1;
      B[i][j] = 2;
    }
  }

  //multiply matrices

  printf("Multiply matrices %d times...\n", numreps);
  for (i=0; i<numreps; i++)
  {
    gettimeofday(&tv1, &tz);
    Multiply(n,A,B,C);
    gettimeofday(&tv2, &tz);
    elapsed += (double) (tv2.tv_sec-tv1.tv_sec) + (double) (tv2.tv_usec-tv1.tv_usec) * 1.e-6; 
  }
  printf("Time = %lf \n",elapsed);

  //deallocate memory

  free(A[0]);
  free(A);
  free(B[0]);
  free(B);
  free(C[0]);
  free(C);
  return 0;
}