[bugfix][CoarsestVolume] catch exception in case `father` is not

implemented.

dune/fem-dg/operator/adaptation/utility.hh

@@ -161,13 +161,24 @@ namespace Fem
     typedef std::pair< double, double > VolumePairType;
 
     template <class Entity>
-    double findCoarsestVolume( const Entity& entity, const bool hasGridHierarchy ) const
+    double findCoarsestVolume( const Entity& entity, const bool hasGridHierarchy, bool& hasFather ) const
     {
       // go to father, if possible
       // otherwise write min and max volume on backup/restore
-      if( hasGridHierarchy && entity.level() > 0 )
+      if( hasGridHierarchy && (entity.level() > 0) && hasFather )
       {
-        return findCoarsestVolume( entity.father(), hasGridHierarchy );
+        double vol = 0.0;
+        // grids without hierarchy do not implement father method,
+        // but throw and exception instead
+        try {
+          vol = findCoarsestVolume( entity.father(), hasGridHierarchy, hasFather );
+        }
+        catch (const Dune::NotImplemented& e )
+        {
+          hasFather = false;
+          vol = entity.geometry().volume();
+        }
+        return vol;
       }
       else  // return entity's volume
         return entity.geometry().volume();
@@ -181,6 +192,7 @@ namespace Fem
       typedef typename GridPart :: GridType GridType ;
 
       const bool hasGridHierarchy = Fem :: GridPartCapabilities :: hasGrid< GridPart > :: v;
+      bool hasFather = true; // will be set to false if father () fails
 
       double weight = Dune::DGFGridInfo<GridType>::refineWeight();
       // if weight is not set, use 1/(2^d)
@@ -194,7 +206,7 @@ namespace Fem
 
       for( const auto& en : elements( gridPart ) )
       {
-        const double volume = findCoarsestVolume( en, hasGridHierarchy );
+        const double volume = findCoarsestVolume( en, hasGridHierarchy, hasFather );
         minVolume[ 0 ] = std::min( minVolume[ 0 ], volume );
         maxVolume[ 0 ] = std::max( maxVolume[ 0 ], volume );
       }