Made the resizable_tensor's assignment operator work in a more sensible way.

dlib/dnn/tensor.h

@@ -332,31 +332,12 @@ namespace dlib
             const matrix_exp<EXP>& item
         )
         {
+            if (!(num_samples() == item.nr() && k()*nr()*nc() == item.nc()))
                 set_size(item.nr(), item.nc());
             tensor::operator=(item);
             return *this;
         }
 
-        template <typename EXP>
-        resizable_tensor& operator+= (
-            const matrix_exp<EXP>& item
-        )
-        {
-            set_size(item.nr(), item.nc());
-            tensor::operator+=(item);
-            return *this;
-        }
-
-        template <typename EXP>
-        resizable_tensor& operator-= (
-            const matrix_exp<EXP>& item
-        )
-        {
-            set_size(item.nr(), item.nc());
-            tensor::operator-=(item);
-            return *this;
-        }
-
         void set_size(
             long n_, long k_ = 1, long nr_ = 1, long nc_ = 1
         )

dlib/dnn/tensor_abstract.h

@@ -495,6 +495,9 @@ namespace dlib
             requires
                 - item contains float values
             ensures
+                - if (num_samples() == item.nr() && k()*nr()*nc() == item.nc()) then
+                    - the dimensions of this tensor are not changed
+                - else
                     - #num_samples() == item.nr()
                     - #k() == item.nc()
                     - #nr() == 1
@@ -502,38 +505,6 @@ namespace dlib
                 - Assigns item to *this tensor by performing:
                   set_ptrm(host(), num_samples(), k()*nr()*nc()) = item;
         !*/
-
-        template <typename EXP>
-        resizable_tensor& operator+= (
-            const matrix_exp<EXP>& item
-        );
-        /*!
-            requires
-                - item contains float values
-            ensures
-                - #num_samples() == item.nr()
-                - #k() == item.nc()
-                - #nr() == 1
-                - #nc() == 1
-                - Adds item to *this tensor by performing:
-                  set_ptrm(host(), num_samples(), k()*nr()*nc()) += item;
-        !*/
-
-        template <typename EXP>
-        resizable_tensor& operator-= (
-            const matrix_exp<EXP>& item
-        );
-        /*!
-            requires
-                - item contains float values
-            ensures
-                - #num_samples() == item.nr()
-                - #k() == item.nc()
-                - #nr() == 1
-                - #nc() == 1
-                - Subtracts item from *this tensor by performing:
-                  set_ptrm(host(), num_samples(), k()*nr()*nc()) -= item;
-        !*/
     };
 
     void serialize(const tensor& item, std::ostream& out);