MatrixXf mat(2,2); 
mat << 1, 2,  4, 7;
cout << "Here is the matrix mat:\n" << mat << endl << endl;

mat = 2 * mat;
cout << "After 'mat = 2 * mat', mat = \n" << mat << endl << endl;


mat = mat - MatrixXf::Identity(2,2);
cout << "After the subtraction, it becomes\n" << mat << endl << endl;


ArrayXXf arr = mat;
arr = arr.square();
cout << "After squaring, it becomes\n" << arr << endl << endl;

// Combining all operations in one statement:
mat << 1, 2,  4, 7;
mat = (2 * mat - MatrixXf::Identity(2,2)).array().square();
cout << "Doing everything at once yields\n" << mat << endl << endl;