adding comment on negation

theano/tensor/basic.py

@@ -4423,6 +4423,9 @@ class Reshape(Op):
             return [requ]
         else:
             new_dims = [node.inputs[1][i] for i in xrange(self.ndim)]
+            # since new_dims has one negative value (-1), the
+            # multiplication of all values should be negated
+            # to give a positive value
             return [tuple([switch(eq(new_dims[i], -1),
                                   theano.tensor.mul(*ishapes[0]) //
                                   (-theano.tensor.mul(*new_dims)),