[eigen] why does the result of the col member function behave so different?

[Helmut Jarausch <jarausch@xxxxxxxxxxxxxxxxxxx>]

Hi,

I was surprised to find out that the following (marked) statements do 
not work with Eigen 3.0 .
Many thanks for a comment,
Helmut


#include <iostream>
#include <Eigen/Core>
using Eigen::MatrixXd;  using Eigen::VectorXd;

#include <sstream>

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

int main() {
  MatrixXd A(2,2);
  std::istringstream Inp("1 2");
  A << 1,2,3,4;
  // Inp >> A.col(0);              // DOES NOT WORK - why?
  // A.col(1)= A.col(0).square();  // DOES NOT WORK - why?
  std::cout << A << std::endl;
}


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