Re: [ublas] Matrix-vector and vector-vector operations

From: Gunter Winkler (guwi17_at_[hidden])
Date: 2007-05-30 18:12:32

Am Mittwoch, 30. Mai 2007 21:37 schrieb Albert Strasheim:
> Do you have any other suggestions for how to accomplish this without
> needing extra memory?

Another note. The noalias speeds up both version:

* without noalias() (g++ -O2 -DNDEBUG)
for loop: 1.4 s
outer_prod: failed

* with noalias()
for loop: 1.1 s
outer_prod: 1.1 s
(I see _no_ time difference)

#include <boost/timer.hpp>

#include <boost/numeric/ublas/matrix.hpp>
#include <boost/numeric/ublas/matrix_proxy.hpp>
#include <boost/numeric/ublas/vector.hpp>

using namespace boost::numeric::ublas;

int main(int argc, char* argv[])
{
  matrix<double> A(scalar_matrix<double>(196608, 1024, 1.0)); 
  vector<double> b(scalar_vector<double>(A.size2(),1.0));
  scalar_vector<double> e(A.size1(), 1.0);
  boost::timer t;
  t.restart();
#if 1
  noalias( A ) += outer_prod(e, b);
#else
  for (std::size_t i = 0; i < A.size1(); ++i)
  {
    noalias( row(A, i) ) += b;
  }
#endif
  std::cout << "time " << t.elapsed() << " s\n";
  return 0;
}

mfg
Gunter