Method gradient

src/george/kernel_interface.cpp:21–23

    size_t size () const { return kernel_->size(); };
    double value (const double* x1, const double* x2) const { return kernel_->value(x1, x2); };
    void gradient (const double* x1, const double* x2, const unsigned* which, double* grad) const {
      return kernel_->gradient(x1, x2, which, grad);
    };
    void x1_gradient (const double* x1, const double* x2, double* grad) const {
      return kernel_->x1_gradient(x1, x2, grad);
    };