Resolve "Fine to coarse grid filters"

Closes #33 (closed)

hysop/operator/spatial_filtering.py

@@ -89,7 +89,7 @@ class LowpassFilterFrontend(MultiComputationalGraphNodeFrontend):
         check_instance(input_topo,  CartesianTopologyDescriptors)
         check_instance(output_topo, CartesianTopologyDescriptors)
         check_instance(base_kwds, dict, keys=str, allow_none=True)
-        #assert (input_topo != output_topo), "Same topology for input and output."
+        assert (input_topo != output_topo), "Same topology for input and output."
 
         super(LowpassFilterFrontend, self).__init__(input_field=input_field, input_topo=input_topo,
                                                     output_field=output_field, output_topo=output_topo,
@@ -174,9 +174,8 @@ class LowpassFilter(ComputationalGraphNodeGenerator):
             kwds  = self._kwds.copy()
             
             # if source topology is destination topology there is nothing to be done
-            # TODO
-            #if (ttopo == stopo):
-                #continue
+            if (ttopo == stopo):
+                continue
                 
             # else we build a lowpass filter operator
             node = LowpassFilterFrontend(input_variable=(ifield,stopo),