eigen/tut__matrix__assignment__resizing_8cpp_source.html

 MatrixXf a(2,2);

 std::cout << "a is of size " << a.rows() << "x" << a.cols() << std::endl;

 MatrixXf b(3,3);

 a = b;

 std::cout << "a is now of size " << a.rows() << "x" << a.cols() << std::endl;

b
Array< int, 3, 1 > b
Definition: Array_variadic_ctor_cxx11.cpp:2

Eigen::MatrixXf
Matrix< float, Dynamic, Dynamic > MatrixXf
Dynamic×Dynamic matrix of type float.
Definition: Matrix.h:501

a
MatrixXf a(2, 2)