evaluate marker-function only on the barycenter of the element

I had the problem, that an evaluation of the gridfunction only in corners of the element was not working for properly refining the grid.

src/amdis/Marker.inc.hpp

@@ -284,11 +284,10 @@ Flag GridFunctionMarker<Grid, PreGridFct>::markGrid(AdaptInfo& adaptInfo)
     int currentLevel = e.level();
     auto geo = e.geometry();
     auto const& ref = Dune::referenceElement(geo);
-    int targetLevel = 0;
     int codim = ref.dimension;
 
-    for (int i = 0; i < ref.size(codim); i++)
-      targetLevel = std::max(targetLevel, int(std::round(localFct(ref.position(i, codim)))));
+    // evaluate in the center of the element
+    int targetLevel = int(std::round(localFct(ref.position(0,0))));
 
     int m =   ((((targetLevel > currentLevel) && (currentLevel < this->maxRefineLevel_))
                   || (currentLevel < this->minRefineLevel_))