void chkder(const Matrix< Scalar, Dynamic, 1 > &x, const Matrix< Scalar, Dynamic, 1 > &fvec, const Matrix< Scalar, Dynamic, Dynamic > &fjac, Matrix< Scalar, Dynamic, 1 > &xp, const Matrix< Scalar, Dynamic, 1 > &fvecp, int mode, Matrix< Scalar, Dynamic, 1 > &err)