#include <stdlib.h>

void matmul(double a[], double b[], double c[], size_t m, size_t n, size_t p)
{
  size_t i,j,k;
  double r;
  for (i=0; i<n; i++)
    for (j=0; j<p; j++) {
      for (k=0, r=0.0; k<m; k++)
        r += a[i*m+k]*b[k*p+j];
      c[i*p+j]=r;
    }
}