Replace GSL with Eigen?? about weldform HOT 1 OPEN

/** Eigenvalues. NOTE: This function changes the matrix M. */
inline void Eig (Mat3_t & M, Vec3_t & L)
{
    // calculate
    gsl_matrix_view m = gsl_matrix_view_array (M.data(), 3, 3);
    gsl_vector * eval = gsl_vector_alloc      (3);
    gsl_eigen_symm_workspace * w = gsl_eigen_symm_alloc (3);
    gsl_eigen_symm (&m.matrix, eval, w);

    // eigenvalues
    L = gsl_vector_get(eval,0), gsl_vector_get(eval,1), gsl_vector_get(eval,2);

    // clean up
    gsl_eigen_symm_free (w);
    gsl_vector_free     (eval);
}