Function der_rosen

dlib/test/optimization.cpp:88–95

    }

    matrix<double,2,1> der_rosen ( const matrix<double,2,1>& x)
    {
        ++total_count;
        matrix<double,2,1> res;
        res(0) = -400*x(0)*(x(1)-x(0)*x(0)) - 2*(1-x(0));
        res(1) = 200*(x(1)-x(0)*x(0));
        return res;
    }

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