
      static double mp_pow(_cimg_math_parser& mp) {
        const double v = _mp_arg(2), p = _mp_arg(3);
        return std::pow(v,p);

      static double mp_pow(_cimg_math_parser& mp) {
        const double v = _mp_arg(2), p = _mp_arg(3);
        return std::pow(v,p);