From 3a50b08179f86cc167c70917897bd5accd5e56ea Mon Sep 17 00:00:00 2001
From: augustin64 <me.git@augustin64.fr>
Date: Fri, 10 Mar 2023 18:19:23 +0100
Subject: [PATCH] Add max_pooling backward

---
 src/cnn/backpropagation.c         | 32 ++++++++++++++++++++++++++++++-
 src/cnn/cnn.c                     |  4 ++--
 src/cnn/include/backpropagation.h |  6 ++++++
 3 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/src/cnn/backpropagation.c b/src/cnn/backpropagation.c
index 4a2045d..8a89f59 100644
--- a/src/cnn/backpropagation.c
+++ b/src/cnn/backpropagation.c
@@ -1,3 +1,5 @@
+#include <stdio.h>
+#include <float.h>
 #include <math.h>
 
 #include "include/backpropagation.h"
@@ -30,7 +32,6 @@ void softmax_backward_cross_entropy(float* input, float* output, int size) {
 void backward_average_pooling(float*** input, float*** output, int input_width, int output_width, int depth) {
     /* Input et output ont la même profondeur (depth) */
 
-    //int size = output_width - input_width +1;
     int size = input_width/output_width; // Taille du pooling
     int n = size*size; // Nombre d'éléments dans le pooling
 
@@ -52,6 +53,35 @@ void backward_average_pooling(float*** input, float*** output, int input_width,
     }
 }
 
+void backward_max_pooling(float*** input, float*** output, int input_width, int output_width, int depth) {
+    int size = input_width/output_width;
+
+    float m; // Maximum
+    int a_max, b_max; // Indices du maximum
+
+    for (int i=0; i < depth; i++) {
+        for (int j=0; j < output_width; j++) {
+            for (int k=0; k < output_width; k++) {
+                m = -FLT_MAX;
+                a_max = -1;
+                b_max = -1;
+
+                for (int a=0; a < size; a++) {
+                    for (int b=0; b < size; b++) {
+                        if (input[i][size*j +a][size*k +b] > m) {
+                            m = input[i][size*j +a][size*k +b];
+                            a_max = a;
+                            b_max = b;
+                            input[i][size*j +a][size*k +b] = 0;
+                        }
+                    }
+                }
+                input[i][size*j +a_max][size*k +b_max] = output[i][j][k];
+            }
+        }
+    }
+}
+
 void backward_dense(Kernel_nn* ker, float* input, float* input_z, float* output, int size_input, int size_output, ptr d_function, int is_first) {
     // Bias
     for (int j=0; j < size_output; j++) {
diff --git a/src/cnn/cnn.c b/src/cnn/cnn.c
index a9cdd10..c18a37b 100644
--- a/src/cnn/cnn.c
+++ b/src/cnn/cnn.c
@@ -18,7 +18,7 @@
 
 int indice_max(float* tab, int n) {
     int indice = -1;
-    float maxi = FLT_MIN;
+    float maxi = -FLT_MAX;
 
     for (int i=0; i < n; i++) {
         if (tab[i] > maxi) {
@@ -187,7 +187,7 @@ void backward_propagation(Network* network, int wanted_number) {
             if (k_i->pooling == AVG_POOLING) {
                 backward_average_pooling(input, output, input_width, output_width, input_depth); // Depth pour input et output a la même valeur
             } else {
-                printf_error("La backpropagation de ce pooling n'est pas encore implémentée\n");
+                backward_max_pooling(input, output, input_width, output_width, input_depth); // Depth pour input et output a la même valeur
             }
         }
     }
diff --git a/src/cnn/include/backpropagation.h b/src/cnn/include/backpropagation.h
index 15a6a85..dea99ff 100644
--- a/src/cnn/include/backpropagation.h
+++ b/src/cnn/include/backpropagation.h
@@ -31,6 +31,12 @@ void softmax_backward_cross_entropy(float* input, float* output, int size);
 */
 void backward_average_pooling(float*** input, float*** output, int input_width, int output_width, int depth);
 
+/*
+* Transfert les informations d'erreur à travers une couche de max pooling
+* en considérant cross_entropy comme fonction d'erreur
+*/
+void backward_max_pooling(float*** input, float*** output, int input_width, int output_width, int depth);
+
 /*
 * Transfert les informations d'erreur à travers une couche fully connected
 */