eigen_reshape_test.cc

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

using namespace std;
using namespace Eigen;

int main() {
  MatrixXd A(2, 2);
  A << 1, 2, 3, 4;
  cout << A << endl << endl;
  A.resize(4, 1);
  cout << A << endl << endl;

  MatrixXd B(2, 2);
  B << 1, 2, 3, 4;
  cout << B << endl << endl;
  B.conservativeResize(4, 1);
  cout << B << endl << endl;

  return 0;
}

/*
Output:

1 2
3 4

1
3
2
4

1 2
3 4

1
3
0
0

*/