craffael

Okay I've visualized the square_quads.msh using ParaView and second order elements:  Then if we refine it once:  As you can see there is not really a difference between...

@hiptmair @anianruoss What do you think?

Yes, as a skeleton examples are very useful. But we should strive to have not too many of those examples because, most of them will probably look very similarly. I...

Aha I see, that wasn't clear to me when I looked at the header file and also @TobiasRohner started using one of the methods without knowing that these are not...

@victorapm I've setup a small test program which shows the issue. Along with the test program I provide you matrices for four different mesh sizes (the mesh size is halfed...

@victorapm It would be great if you could have a look. I'm still a bit puzzled by the fact that a few additional basis functions can trouble AMG that much....

Hi all a few comments: - AMS/ADS are not applicable, it is a scalar valued Laplace problem. - I've already tried various (in)complete Schur complement approaches, but they are quite...

@liruipeng I try to summarize a bit what I've tried. For the discussion lets assume the system matrix has the following block structure:  Where C is small `n x...