[Boost-users] uBLAS and stl algorithms

14 Apr 2005

      Hi List Members

I have data stored in an matrix. Now, i want to acces the data of the matrix 
row-wise. because i want to access it in a sorted manner (without moving the 
matrix entries around), i make a stl-vector of matrix_rows. This works fine. 
But if i now use the stl algorithms to sort the stl-vector by a certain 
criteria, then it happens, that the algorithm is making several copies of a 
singe vector entry and overwriting other entries.

Can anyone give me a tipp, what i'm doing wrong?

----------------------------

Here is an example code:

#include<iostream>
#include<vector>
#include<algorithm>
#include<cmath>
#include<boost/numeric/ublas/matrix.hpp>
#include<boost/numeric/ublas/io.hpp>

namespace num=boost::numeric::ublas;

template <int N>
class Ordering
{
public:
  bool operator()(num::matrix_row<num::matrix<double> > A, 
num::matrix_row<num::matrix<double> > B)
  {
    if (A(N) < B(N) ) return true;
    else return false;
  }
};

int main(int argc, char* argv[])
{  
  const int N = 10000; 
  const int M = 4;

  num::matrix<double> Matrix(N, M);

  for (int i = 0; i < Matrix.size1(); i++)
    {
      for (int j = 0; j < Matrix.size2(); j++)
	{
	  Matrix(i, j) = drand48();
	}
    }

  std::vector<num::matrix_row<num::matrix<double> > > MyAccess;

  for (int i = 0; i < Matrix.size1(); i++)
    {
      MyAccess.push_back(num::matrix_row<num::matrix<double> >(Matrix, i) );
    }

  for (int i = 0; i < Matrix.size1(); i++)
    {
      std::cout << MyAccess[i] << std::endl;
    }

  std::sort(MyAccess.begin(), MyAccess.end(), Ordering<0>() );

  for (int i = 0; i < Matrix.size1(); i++)
    {
      std::cout << MyAccess[i] << std::endl;
    }
}

[Boost-users] uBLAS and stl algorithms

Pascal Bauer