Epetra: Error in matrix-matrix multiplication

[searhein]

Question

@trilinos/epetra
@trilinos/xpetra
@trilinos/shylu

First, I should not that I am using Epetra through the Xpetra interface in FROSch. My question is the following:

Previously, I constructed a specific Epetra_CrsMatrix (through an Xpetra::Matrix) without specifying a column map. Now, I added a column map to the call of the constructor in order to be able to assembly the matrix using local indices. This works smoothly.
However, at a later point in the code, I am multiplying another Epetra_CrsMatrix (Xpetra::Matrix) with this matrix using Xpetra::MatrixMatrix<>::Multiply(). At this point the program, terminates with the error:

Epetra_MpiDistributor::CreateRecvStructures_ expected RemotePIDs to be in sorted order

I am very surprised about this, also because I do not obtain this error using Tpetra instead. For now, I added an if statement to differentiate between Epetra and Tpetra; see the changes to the file packages/shylu/shylu_dd/frosch/src/CoarseSpaces/FROSch_CoarseSpace_def.hpp (lines 170-193) in my PR #8825. This should be fine for now, however, it would be great to understand how I could also get this running with Epetra.

[csiefer2]

There's an assumption that the column map is in "Aztec" ordering, which is as follows:

1. All the "local rows" (aka rows which in the domain map) first.
2. Off-rank rows are ordered by owning PID and sub-sorted by GID.

[searhein]

@csiefer2 Thanks for the explanation. Is there a way to automatically re-order the map accordingly?

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