Member Dune::VTKWriter< GridView >::addCellData (F &&f, VTK::FieldInfo vtkFieldInfo): f may also be a VTKFunction object, but you are strongly discouraged from using VTKFunctions.
Member Dune::VTKWriter< GridView >::addVertexData (F &&f, VTK::FieldInfo vtkFieldInfo): f may also be a VTKFunction object, but you are strongly discouraged from using VTKFunctions.