Added set_all_bn_running_stats_window_sizes() and also changed the default

batch normalization running stats window size from 1000 to 100.

dlib/dnn/layers.h

@@ -718,12 +718,19 @@ namespace dlib
             bias_learning_rate_multiplier(1),
             bias_weight_decay_multiplier(1),
             eps(eps_)
-        {}
+        {
+            DLIB_CASSERT(window_size > 0, "The batch normalization running stats window size can't be 0.");
+        }
 
-        bn_() : bn_(1000) {}
+        bn_() : bn_(100) {}
 
         layer_mode get_mode() const { return mode; }
         unsigned long get_running_stats_window_size () const { return running_stats_window_size; }
+        void set_running_stats_window_size (unsigned long new_window_size ) 
+        { 
+            DLIB_CASSERT(new_window_size > 0, "The batch normalization running stats window size can't be 0.");
+            running_stats_window_size = new_window_size; 
+        }
         double get_eps() const { return eps; }
 
         double get_learning_rate_multiplier () const  { return learning_rate_multiplier; }
@@ -776,8 +783,10 @@ namespace dlib
             if (sub.get_output().num_samples() > 1)
             {
                 const double decay = 1.0 - num_updates/(num_updates+1.0);
-                if (num_updates <running_stats_window_size)
                 ++num_updates;
+                if (num_updates > running_stats_window_size)
+                    num_updates = running_stats_window_size;
+
                 if (mode == FC_MODE)
                     tt::batch_normalize(eps, output, means, invstds, decay, running_means, running_variances, sub.get_output(), g, b);
                 else 
@@ -867,6 +876,7 @@ namespace dlib
             else
                 out << "bn_fc   ";
             out << " eps="<<item.eps;
+            out << " running_stats_window_size="<<item.running_stats_window_size;
             out << " learning_rate_mult="<<item.learning_rate_multiplier;
             out << " weight_decay_mult="<<item.weight_decay_multiplier;
             out << " bias_learning_rate_mult="<<item.bias_learning_rate_multiplier;
@@ -882,6 +892,7 @@ namespace dlib
                 out << "<bn_fc";
 
             out << " eps='"<<item.eps<<"'";
+            out << " running_stats_window_size='"<<item.running_stats_window_size<<"'";
             out << " learning_rate_mult='"<<item.learning_rate_multiplier<<"'";
             out << " weight_decay_mult='"<<item.weight_decay_multiplier<<"'";
             out << " bias_learning_rate_mult='"<<item.bias_learning_rate_multiplier<<"'";
@@ -918,6 +929,56 @@ namespace dlib
     template <typename SUBNET>
     using bn_fc = add_layer<bn_<FC_MODE>, SUBNET>;
 
+// ----------------------------------------------------------------------------------------
+
+    namespace impl
+    {
+        class visitor_bn_running_stats_window_size
+        {
+        public:
+
+            visitor_bn_running_stats_window_size(unsigned long new_window_size_) : new_window_size(new_window_size_) {}
+
+            template <typename T>
+            void set_window_size(T&) const
+            {
+                // ignore other layer detail types
+            }
+
+            template < layer_mode mode >
+            void set_window_size(bn_<mode>& l) const
+            {
+                l.set_running_stats_window_size(new_window_size);
+            }
+
+            template<typename input_layer_type>
+            void operator()(size_t , input_layer_type& )  const
+            {
+                // ignore other layers
+            }
+
+            template <typename T, typename U, typename E>
+            void operator()(size_t , add_layer<T,U,E>& l)  const
+            {
+                set_window_size(l.layer_details());
+            }
+
+        private:
+
+            unsigned long new_window_size;
+        };
+    }
+
+    template <typename net_type>
+    void set_all_bn_running_stats_window_sizes (
+        net_type& net,
+        unsigned long new_window_size
+    )
+    {
+        visit_layers(net, impl::visitor_bn_running_stats_window_size(new_window_size));
+    }
+
+// ----------------------------------------------------------------------------------------
 // ----------------------------------------------------------------------------------------
 
     enum fc_bias_mode

dlib/dnn/layers_abstract.h

@@ -922,7 +922,7 @@ namespace dlib
         /*!
             ensures
                 - #get_mode() == mode
-                - #get_running_stats_window_size()      == 1000
+                - #get_running_stats_window_size()      == 100
                 - #get_learning_rate_multiplier()       == 1
                 - #get_weight_decay_multiplier()        == 0
                 - #get_bias_learning_rate_multiplier()  == 1
@@ -937,6 +937,7 @@ namespace dlib
         /*!
             requires
                 - eps > 0
+                - window_size > 0
             ensures
                 - #get_mode() == mode 
                 - #get_running_stats_window_size()     == window_size
@@ -985,6 +986,16 @@ namespace dlib
                   the running average.
         !*/
 
+        void set_running_stats_window_size (
+            unsigned long new_window_size
+        );
+        /*!
+            requires
+                - new_window_size > 0
+            ensures
+                - #get_running_stats_window_size() == new_window_size
+        !*/
+
         double get_learning_rate_multiplier(
         ) const;  
         /*!
@@ -1078,6 +1089,23 @@ namespace dlib
     template <typename SUBNET>
     using bn_fc = add_layer<bn_<FC_MODE>, SUBNET>;
 
+// ----------------------------------------------------------------------------------------
+
+    template <typename net_type>
+    void set_all_bn_running_stats_window_sizes (
+        const net_type& net,
+        unsigned long new_window_size
+    );
+    /*!
+        requires
+            - new_window_size > 0
+            - net_type is an object of type add_layer, add_loss_layer, add_skip_layer, or
+              add_tag_layer.
+        ensures
+            - Sets the get_running_stats_window_size() field of all bn_ layers in net to
+              new_window_size.
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
     class affine_