[eigen] An insistent plea for an input operator

[Helmut Jarausch <jarausch@xxxxxxxxxxxxxxxxxxx>]

Hi,

I know, I've asked for this feature several month, ago,
but I'm obstinate to ask for it again and again.

Background: I'm teaching C++ for beginners (mathematicians) and
there should be an easy input operator for matrices and vectors.

Currently, I have to patch Eigen (2 or 3) by adding

namespace Eigen {
template<typename Derived>
std::istream & operator >>(std::istream & Inp, MatrixBase<Derived> & m) 
{
  for (int i = 0; i < m.rows(); ++i)
    for (int j = 0; j < m.cols(); j++)
      Inp >> m(i,j);
  
  return Inp;
}

}

to make the following simple program run


int main() {
Eigen::MatrixXi A(2,3);
  std::cerr << "intput 2x3 matrix:\n";
  std::cin >> A;
  std::cout << "I've got:\n" << A << std::endl;
}

I've never understood the objections against adding this.
Pardon for being such obstinate,
Helmut.

My problem is, that students download Eigen themselves and forget about
adding these few lines.

-- 
Helmut Jarausch

Lehrstuhl fuer Numerische Mathematik
RWTH - Aachen University
D 52056 Aachen, Germany