dropout % backward() doesn't need input from the previous layer

Author: milancurcic

src/nf/nf_dropout_layer.f90

@@ -48,14 +48,12 @@ end function dropout_layer_cons
 
   interface
 
-    pure module subroutine backward(self, input, gradient)
+    pure module subroutine backward(self, gradient)
       !! Apply the backward gradient descent pass.
       !! Only weight and bias gradients are updated in this subroutine,
       !! while the weights and biases themselves are untouched.
       class(dropout_layer), intent(in out) :: self
         !! Dropout layer instance
-      real, intent(in) :: input(:)
-        !! Input from the previous layer
       real, intent(in) :: gradient(:)
         !! Gradient from the next layer
     end subroutine backward

src/nf/nf_dropout_layer_submodule.f90

@@ -59,18 +59,10 @@ module subroutine forward(self, input)
   end subroutine forward
 
 
-  pure module subroutine backward(self, input, gradient)
+  pure module subroutine backward(self, gradient)
     class(dropout_layer), intent(in out) :: self
-    real, intent(in) :: input(:)
     real, intent(in) :: gradient(:)
-
-    if (self % training) then
-      ! Backpropagate gradient through dropout mask
-      self % gradient = gradient * self % mask * self % scale
-    else
-      ! In inference mode, pass through the gradient unchanged
-      self % gradient = gradient
-    end if
+    self % gradient = gradient * self % mask * self % scale
   end subroutine backward
 
 end submodule nf_dropout_layer_submodule 

src/nf/nf_layer_submodule.f90

@@ -40,16 +40,8 @@ pure module subroutine backward_1d(self, previous, gradient)
         end select
 
       type is(dropout_layer)
-
         ! Upstream layers permitted: input1d, dense, dropout, flatten
-        select type(prev_layer => previous % p)
-          type is(input1d_layer)
-            call this_layer % backward(prev_layer % output, gradient)
-          type is(dense_layer)
-            call this_layer % backward(prev_layer % output, gradient)
-          type is(flatten_layer)
-            call this_layer % backward(prev_layer % output, gradient)
-        end select
+        call this_layer % backward(gradient)
 
       type is(flatten_layer)