MueLu: filtered matrix lumping may be buggy
Created by: aprokop
@trilinos/muelu
Summary
A potential bug in MueLu's FilteredAFactory lumping procedure affecting both non-kokkos and kokkos branches.
Description
In MueLu_FilteredAFactory_def.hpp the lumping procedure seem to only use local indices for determining which element is diagonal. This is a problem for situations when row map and column map do not "match". In that situation, the dropped entries may be added to non-diagonal element thus exacerbating situation.
Who is affected
Potentially anybody using non-standard column map in conjuction with filtering. Panzer?
How to address
As a first step, we need to identify if anybody is getting hit by this. I propose adding a check isSameMap similarly to TentativePFactory. If we do get somebody affected, we need to decide what to do. Going to global indices is going to be very expensive.