[eigen] Vector's -= operator does not seem to work

[Hung Dang]

Hi,

I try some Eigen examples (see below) and the -= operator is not 
supported. Is there any way to make it work without creating a constant 
vector?

Thank a lot,

Hung

    Matrix2d a;
    a << 1, 2, 3, 4;
    Vector3d v(1, 2, 3);
    std::cout << "a * 2.5 =\n" << a * 2.5 << std::endl;
    std::cout << "0.1 * v =\n" << 0.1 * v << std::endl;
    std::cout << "Doing v *= 2;" << std::endl;

    v *= 2;
    std::cout << "Now v =\n" << v << std::endl;

    // Does not work
    // v -= 2;
    // std::cout << "Now v =\n" << v << std::endl;