[ublas] prod time - sparse matrix

From: Fred (hakonbh_at_[hidden])
Date: 2006-08-16 15:18:05

Hi,

Could you help to decrease time of prod when I use the typedef defined in
the code below?

#include <boost/timer.hpp>
#include <boost/numeric/ublas/matrix.hpp>
#include <boost/numeric/ublas/matrix_sparse.hpp>
#include <boost/numeric/ublas/matrix_proxy.hpp>
#include <boost/numeric/ublas/vector_sparse.hpp>
#include <boost/numeric/ublas/vector_proxy.hpp>
#include <boost/numeric/ublas/vector_of_vector.hpp>
#include <boost/numeric/ublas/operation.hpp>
#include <boost/numeric/ublas/io.hpp>

int main () {
    using namespace boost::numeric::ublas;

    typedef generalized_vector_of_vector< double, row_major,
        boost::numeric::ublas::vector< compressed_vector<double> > > matrix;
    typedef compressed_vector<double> vec_d;

//    typedef matrix<double> matrix;
//    typedef vector<double> vec_d;

    boost::timer  t1;
    double t_final;

    matrix m(3,3);
    vec_d v(3);
    vec_d result;
    for (unsigned i = 0; i < std::min (m.size1 (), v.size ()); ++ i) {
        for (unsigned j = 0; j < m.size2 (); ++ j)
            m (i, j) = 3 * i + j;
        v (i) = i;
    }

    std::cout << m << std::endl;
    std::cout << v << std::endl;

    int counter = 0;
    for(int n=0; n<20 ; ++n)
    {
       for(int i=0; i<200 ; ++i)
       {
          t1.restart();
          result = prod(m, v);
          t_final = t1.elapsed();

          if (t_final > 0.01)
          {
             std::cout << "time = " << t_final << std::endl;
             counter++;
          }
       }
    }
    std::cout << "counter = " << counter << std::endl;
}

I don't understand why prod spends "0 sec" in some iterations and
"0.016sec" (in my computer) if variables are always the same...

Thank you for your time!

Frederico B. Teixeira
---
UFMG, Brazil