Method get_gradient

dlib/cuda/cpu_dlib.cpp:2749–2829

        }

        void pooling::get_gradient(
            const tensor& gradient_input, 
            const tensor& dest,
            const tensor& src,
            tensor& grad 
        )
        {
            DLIB_CASSERT(have_same_dimensions(gradient_input,dest));
            DLIB_CASSERT(have_same_dimensions(src,grad));


            if (src.size() == 0)
            {
                return;
            }


            auto gi = gradient_input.host();
            auto g = grad.host();
            const long x_offset = window_width/2 - padding_x;
            const long y_offset = window_height/2 - padding_y;
            if (does_max_pooling())
            {
                for (long n = 0; n < dest.num_samples(); ++n)
                {
                    for (long k = 0; k < dest.k(); ++k)
                    {
                        auto simg = image_plane(src,n,k);
                        auto gimg = g + (n*grad.k() + k)*grad.nr()*grad.nc();
                        auto giimg = gi + (n*dest.k() + k)*dest.nr()*dest.nc();
                        auto imgbox = get_rect(simg);

                        for (long r = 0; r < dest.nr(); ++r)
                        {
                            for (long c = 0; c < dest.nc(); ++c)
                            {
                                auto win = centered_rect(c*stride_x+x_offset,
                                    r*stride_y+y_offset,
                                    window_width,
                                    window_height).intersect(imgbox);
                                auto p = max_point(subm(simg,win))+win.tl_corner();
                                gimg[p.y()*grad.nc()+p.x()] += giimg[r*dest.nc()+c];
                            }
                        }
                    }
                }
            }
            else
            {
                for (long n = 0; n < dest.num_samples(); ++n)
                {
                    for (long k = 0; k < dest.k(); ++k)
                    {
                        auto simg = image_plane(src,n,k);
                        auto gimg = g + (n*grad.k() + k)*grad.nr()*grad.nc();
                        auto giimg = gi + (n*dest.k() + k)*dest.nr()*dest.nc();
                        auto imgbox = get_rect(simg);