Computing an inner product of tuples represented as vectors

   
 

#include <vector>
#include <iostream>
using namespace std;

int main()
{
  const long N = 600000; // Length of tuples x and y
  const long S = 10;     // Sparseness factor

  vector<double> x(N), y(N);


  for (long k = 0; 3 * k * S < N; ++k)
    x[3 * k * S] = 1.0;
  for (long k = 0; 5 * k * S < N; ++k)
    y[5 * k * S] = 1.0;

  double sum = 0.0;
  for (long k = 0; k < N; ++k)
    sum += x[k] * y[k];

  cout << sum << endl;
  return 0;
}

/* 
4000

 */

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Computing an inner product of tuples represented as vectors : vector « Vector « C++

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