Exchange troubled cell

Some more features for LimitPass.

dune/fem-dg/operator/dg/dgpyoperator.hh

@@ -97,6 +97,7 @@ namespace Fem
     typedef DGAdaptationIndicatorOperator< OpTraits >                       IndicatorType;
     typedef Estimator< DestinationType, typename ModelType::ProblemType >   GradientIndicatorType ;
     typedef AdaptIndicator< IndicatorType, GradientIndicatorType >          AdaptIndicatorType;
+
     typedef typename FullOperatorType :: TroubledCellIndicatorType          TroubledCellIndicatorType;
 
     // solver selection, available fem, istl, petsc, ...
@@ -198,6 +199,12 @@ namespace Fem
 
     double timeStepEstimate() const { return fullOperator_.timeStepEstimate(); }
 
+    //! return number of interior elements visited by the operator
+    inline size_t gridSizeInterior() const
+    {
+      return std::max( fullOperator_.numberOfElements(), explOperator_.numberOfElements() );
+    }
+
     //// End Methods from SpaceOperatorInterface /////
 
   protected: