source: pacpussensors/trunk/Vislab/lib3dv/eigen/Eigen-install/doc/snippets/compile_MatrixBase_eval.cpp@ 136

#include <Eigen/Dense>
#include <iostream>

using namespace Eigen;
using namespace std;

int main(int, char**)
{
  cout.precision(3);
  Matrix2f M = Matrix2f::Random();
Matrix2f m;
m = M;
cout << "Here is the matrix m:" << endl << m << endl;
cout << "Now we want to copy a column into a row." << endl;
cout << "If we do m.col(1) = m.row(0), then m becomes:" << endl;
m.col(1) = m.row(0);
cout << m << endl << "which is wrong!" << endl;
cout << "Now let us instead do m.col(1) = m.row(0).eval(). Then m becomes" << endl;
m = M;
m.col(1) = m.row(0).eval();
cout << m << endl << "which is right." << endl;

  return 0;
}