in 5bc123e3 I added a new test for the P1ElementwiseMassOperator. That test fails, which is why I added it, to show that currently there is problem with the (partial) implementation of the P1ElementwiseOperator class. Though actually the problem seems to be in the applyElementwise() methods of VertexDoFMacroVertex.hpp and VertexDoFMacroEdge.hpp. The stencils are not assembled correctly, see below. For example the stencils for DoFs on edge ID 6 should be identical to the face stencils in the tested setup. For the faceStencils everything seems to be okay. I'll try to fix that. Should teach me more on the tinyHHG internals.