#include        <stdio.h>

#define        m        10
#define        n        20

int main(int argc, char *argv[])
{
  double a[m][n], x[n], y[m];
  int    i, j;

  for ( i = 0; i < m; i++ )
  {
    y[i] = 0;
    for ( j = 0; j < n; j++ ) 
      y[i] = y[i] + a[i][j]*x[j];
  }
  
  for ( i = 0; i < m; i++ )
    y[i] = 0;
  for ( j = 0; j < n; j++ )
  {
    for ( i = 0; i < m; i++ )
      y[i] = y[i] + a[i][j]*x[j];
  }
  
}