Figured out the *undocumented* requirements for calling cuDNN's

cudnnAddTensor() function and updated the specs and asserts accordingly.

dlib/dnn/cpu_dlib.cpp

@@ -76,11 +76,21 @@ namespace dlib
         )
         {
             DLIB_CASSERT(
-                  (dest.num_samples()==src.num_samples() || src.num_samples()==1) &&
-                  (dest.nr()==src.nr() || src.nr()==1) &&
-                  (dest.nc()==src.nc() || src.nc()==1) &&
-                  (dest.k()==src.k()   || src.k()==1) && 
-                  is_same_object(src,dest) == false , "");
+                  (have_same_dimensions(src, dest) ||
+                  (src.num_samples()==1 && src.k()==dest.k() && src.nr()==1 && src.nc()==1) ||
+                  (src.num_samples()==1 && src.k()==dest.k() && src.nr()==dest.nr() && src.nc()==dest.nc()) ||
+                  (src.num_samples()==1 && src.k()==1 && src.nr()==dest.nr() && src.nc()==dest.nc())) &&
+                  is_same_object(src,dest) == false , 
+                    "\n\t dest.num_samples(): " << dest.num_samples()
+                    <<"\n\t dest.k():           " << dest.k()
+                    <<"\n\t dest.nr():          " << dest.nr()
+                    <<"\n\t dest.nc():          " << dest.nc()
+                    <<"\n\t src.num_samples():  " << src.num_samples()
+                    <<"\n\t src.k():            " << src.k()
+                    <<"\n\t src.nr():           " << src.nr()
+                    <<"\n\t src.nc():           " << src.nc()
+                    );
+
 
             if (beta == 0 && alpha == 0)
             {

dlib/dnn/cudnn_dlibapi.cpp

@@ -197,11 +197,20 @@ namespace dlib
         )
         {
             DLIB_CASSERT(
-                  (dest.num_samples()==src.num_samples() || src.num_samples()==1) &&
-                  (dest.nr()==src.nr() || src.nr()==1) &&
-                  (dest.nc()==src.nc() || src.nc()==1) &&
-                  (dest.k()==src.k()   || src.k()==1) &&
-                  is_same_object(src,dest) == false , "");
+                  (have_same_dimensions(src, dest) ||
+                  (src.num_samples()==1 && src.k()==dest.k() && src.nr()==1 && src.nc()==1) ||
+                  (src.num_samples()==1 && src.k()==dest.k() && src.nr()==dest.nr() && src.nc()==dest.nc()) ||
+                  (src.num_samples()==1 && src.k()==1 && src.nr()==dest.nr() && src.nc()==dest.nc())) &&
+                  is_same_object(src,dest) == false , 
+                    "\n\t dest.num_samples(): " << dest.num_samples()
+                    <<"\n\t dest.k():           " << dest.k()
+                    <<"\n\t dest.nr():          " << dest.nr()
+                    <<"\n\t dest.nc():          " << dest.nc()
+                    <<"\n\t src.num_samples():  " << src.num_samples()
+                    <<"\n\t src.k():            " << src.k()
+                    <<"\n\t src.nr():           " << src.nr()
+                    <<"\n\t src.nc():           " << src.nc()
+                    );
 
             CHECK_CUDNN(cudnnAddTensor_v3(context(),
                                     &alpha,

dlib/dnn/cudnn_dlibapi.h

@@ -73,10 +73,11 @@ namespace dlib
         );
         /*!
             requires
-                - dest.num_samples()==src.num_samples() || src.num_samples()==1
-                - dest.nr()==src.nr() || src.nr()==1
-                - dest.nc()==src.nc() || src.nc()==1
-                - dest.k()==src.k()   || src.k()==1
+                - One of the following is true: 
+                    - have_same_dimensions(src, dest)
+                    - src.num_samples()==1 && src.k()==dest.k() && src.nr()==1 && src.nc()==1
+                    - src.num_samples()==1 && src.k()==dest.k() && src.nr()==dest.nr() && src.nc()==dest.nc()
+                    - src.num_samples()==1 && src.k()==1 && src.nr()==dest.nr() && src.nc()==dest.nc()
                 - is_same_object(src,dest) == false
             ensures
                 - performs: dest = beta*dest + alpha*src

dlib/dnn/tensor_tools.h

@@ -375,10 +375,11 @@ namespace dlib { namespace tt
     );
     /*!
         requires
-            - dest.num_samples()==src.num_samples() || src.num_samples()==1
-            - dest.nr()==src.nr() || src.nr()==1
-            - dest.nc()==src.nc() || src.nc()==1
-            - dest.k()==src.k()   || src.k()==1
+            - One of the following is true: 
+                - have_same_dimensions(src, dest)
+                - src.num_samples()==1 && src.k()==dest.k() && src.nr()==1 && src.nc()==1
+                - src.num_samples()==1 && src.k()==dest.k() && src.nr()==dest.nr() && src.nc()==dest.nc()
+                - src.num_samples()==1 && src.k()==1 && src.nr()==dest.nr() && src.nc()==dest.nc()
             - is_same_object(src,dest) == false
         ensures
             - performs: dest = beta*dest + alpha*src