template<typename XprType, int Rows, int Cols, int Order>

Eigen::Reshaped class

Expression of a fixed-size or dynamic-size reshape.

This class represents an expression of either a fixed-size or dynamic-size reshape. It is the return type of DenseBase::reshaped(NRowsType,NColsType) and most of the time this is the only way it is used.

However, in C++98, if you want to directly maniputate reshaped expressions, for instance if you want to write a function returning such an expression, you will need to use this class. In C++11, it is advised to use the auto keyword for such use cases.

Here is an example illustrating the dynamic case:

#include <Eigen/Core>
#include <iostream>
using namespace std;
using namespace Eigen;

template<typename Derived>
const Reshaped<const Derived>
reshape_helper(const MatrixBase<Derived>& m, int rows, int cols)
{
  return Reshaped<const Derived>(m.derived(), rows, cols);
}

int main(int, char**)
{
  MatrixXd m(3, 4);
  m << 1, 4, 7, 10,
       2, 5, 8, 11,
       3, 6, 9, 12;
  cout << m << endl;
  Ref<const MatrixXd> n = reshape_helper(m, 2, 6);
  cout << "Matrix m is:" << endl << m << endl;
  cout << "Matrix n is:" << endl << n << endl;
}

Output:

 1  4  7 10
 2  5  8 11
 3  6  9 12
Matrix m is:
 1  4  7 10
 2  5  8 11
 3  6  9 12
Matrix n is:
 1  3  5  7  9 11
 2  4  6  8 10 12

Here is an example illustrating the fixed-size case:

#include <Eigen/Core>
#include <iostream>
using namespace Eigen;
using namespace std;

template<typename Derived>
Eigen::Reshaped<Derived, 4, 2>
reshape_helper(MatrixBase<Derived>& m)
{
  return Eigen::Reshaped<Derived, 4, 2>(m.derived());
}

int main(int, char**)
{
  MatrixXd m(2, 4);
  m << 1, 2, 3, 4,
       5, 6, 7, 8;
  MatrixXd n = reshape_helper(m);
  cout << "matrix m is:" << endl << m << endl;
  cout << "matrix n is:" << endl << n << endl;
  return 0;
}

Output:

matrix m is:
1 2 3 4
5 6 7 8
matrix n is:
1 3
5 7
2 4
6 8