doc: backpropagation notes added

2 files changed, 21 insertions, 8 deletions

diff --git a/src/nn.c b/src/nn.c
index 87f74ce..d312c29 100644
--- a/src/nn.c
+++ b/src/nn.c
@@ -2,11 +2,12 @@
 
 static void fill_random_weights(double *weights, double *bias, size_t rows, size_t cols);
 
-double * nn_layer_forward(Layer layer, double *input, size_t input_shape[2])
+void nn_layer_forward(Layer layer, double *out, size_t out_shape[2], double *input, size_t input_shape[2])
 {
-    double *out = calloc(input_shape[0] * layer.neurons, sizeof(double));
-    if (out == NULL) {
-        perror("nn_layer_forward() Error");
+    if (out_shape[0] != input_shape[0] || out_shape[1] != layer.neurons) {
+        fprintf(stderr,
+                "nn_layer_forward() Error: out must have (%zu x %zu) dimensions not (%zu x %zu)\n",
+                input_shape[0], layer.neurons, out_shape[0], out_shape[1]);
         exit(1);
     }
 
@@ -22,7 +23,13 @@ double * nn_layer_forward(Layer layer, double *input, size_t input_shape[2])
                 1.0, input, input_shape[1], //alpha X
                 layer.weights, layer.neurons, // W
                 1.0, out, layer.neurons); // beta B
-    return out;
+
+    for (size_t i = 0; i < input_shape[0]; i++) {
+        for (size_t j = 0; j < layer.neurons; j ++) {
+            size_t index = layer.neurons * i + j;
+            out[index] = layer.activation(out[index]);
+        }
+    }
 }
 
 void nn_layer_init_weights(Layer layers[], size_t nmemb, size_t n_inputs)
@@ -58,6 +65,11 @@ void nn_layer_free_weights(Layer *layer, size_t nmemb)
     }
 }
 
+double identity(double x)
+{
+    return x;
+}
+
 double sigmoid(double x)
 {
     return 1 / (1 + exp(-x));
diff --git a/src/nn.h b/src/nn.h
index 88b4462..05ddd28 100644
--- a/src/nn.h
+++ b/src/nn.h
@@ -15,12 +15,13 @@ typedef struct Layer {
     size_t neurons, input_nodes;
 } Layer;
 
-void nn_layer_init_weights(Layer *layer, size_t nmemb, size_t input_cols);
+void nn_layer_init_weights(Layer *layers, size_t nmemb, size_t input_cols);
 void nn_layer_free_weights(Layer *layer, size_t nmemb);
 
-double * nn_layer_forward(Layer layer, double *input, size_t input_shape[2]); //TODO
-double * nn_layer_backward(Layer layer, double *output, size_t out_shape[2]); //TODO
+void nn_layer_forward(Layer layer, double *out, size_t out_shape[2], double *input, size_t input_shape[2]); //TODO
+void nn_layer_backward(Layer *layer, double *out, size_t out_shape[2]); //TODO
 
 double sigmoid(double x);
 double relu(double x);
+double identity(double x);
 #endif