/*
  Program to measure time to carry out matrix-vector product.
  c(i) = sum(a(i,j)*b(j),j=1,...,n) for i=1,...,n
 */

#include <stdio.h>
#include <time.h>
int main()
{
  int i, j;
  printf("Matrix size    Elapsed time [sec] \n");

  for (int k=1; k<=30; k++) {
    // Matrix size
    int n = k*1000;

    // Allocation
    int **a, *b, *c;
    a = new int*[n];
    for (i=0; i<n; i++)
      a[i] = new int[n];
    b = new int[n];
    c = new int[n];

    // Initialization
    for (j=0; j<n; j++)
      for (i=0; i<n; i++)
	a[j][i] = 1;
    for (i=0; i<n; i++)
      b[i] = 1;

    // Start time
    clock_t time0 = clock();

    // Main calculation: matrix-vector product
    for (i=0; i<n; i++) {
      c[i] = 0;
      for (j=0; j<n; j++) {
	c[i] += a[i][j] * b[j];
      }
    }

    // Finish time
    clock_t time1 = clock();

    // Output time
    double eTime = (double)(time1-time0)/CLOCKS_PER_SEC;
    printf("%11d %15.7f\n",n, eTime);

    // Deallocation
    for (int i=0; i<n; i++)
      delete[] a[i];
    delete[] a;
    delete[] b;
    delete[] c;
  }
  return 0;
}