Fix bug in dropout scaling

Co-authored-by: Ricardo Orsi <@ricor07>

Author: milancurcic

src/nf/nf_dropout_layer_submodule.f90

@@ -45,7 +45,7 @@ module subroutine forward(self, input)
     end where
 
     ! Scale factor to preserve the input sum
-    self % scale = sum(input) / sum(self % output)  ! scale == 1/P(keep)
+    self % scale = sum(input) / sum(input * self % mask)
 
     ! Apply dropout mask
     self % output = input * self % mask * self % scale

test/test_dropout_layer.f90

@@ -81,7 +81,7 @@ program test_dropout_layer
     do n = 1, 10000
       output_data = net % predict(input_data)
       ! Check that sum of output matches sum of input within small tolerance
-      if (abs(sum(output_data) - sum(input_data)) > 1e-5) then
+      if (abs(sum(output_data) - sum(input_data)) > 1e-6) then
         ok = .false.
         exit
       end if