conv2d_offset: avoid unnecessary join.

theano/tensor/nnet/conv.py

@@ -53,7 +53,11 @@ def conv2d(input, filters, image_shape=None, filter_shape=None,
       (batch size, nb filters, output row, output col)
     """
     if image_shape and filter_shape:
+      try:
         assert image_shape[1]==filter_shape[1]
+      except:
+        print 'image ', image_shape, ' filters ', filter_shape
+        raise
 
     if filter_shape is not None:
         nkern = filter_shape[0]
@@ -149,7 +153,10 @@ def conv2d_offset(input, filters, image_shape=None, filter_shape=None,
         outputs.append(out)
 
     # Join the outputs on the leading axis.
-    output = tensor.join(1, *outputs)
+    if len(outputs) > 1:
+        output = tensor.join(1, *outputs)
+    else:
+        output = outputs[0] 
 
     outshp = ConvOp.getOutputShape(sub_image_shape[2:], filter_shape[2:], subsample, border_mode)