eigen/doc/snippets/MatrixBase_map_int_int.cpp

int data[4] = {1,3,0,2};
cout << MatrixXi::map(data, 2, 2) << endl;
MatrixXi::map(data, 2, 2) *= 2;
cout << "The data is now:" << endl;
for(int i = 0; i < 4; i++) cout << data[i] << endl;