Ifpack2: column map of OverlappingRowMatrix is not complete

[jhux2]

Bug Report (maybe?)

@trilinos/ifpack2 @csiefer2

Description

Halo rows imported into an OverlappingRowMatrix appear to exclude column indices corresponding to rows that 1) are not in the original local matrix and 2) are not halo rows themselves.

Implications: In order to perform K matvecs with a single communication, the halo must be K layers deep. If this can fixed, then the halo would only have to be K-1 layers deep.

Example

Consider a 1D Poisson matrix on two ranks, 5 rows per process, with overlap 2.

Here is the original "local" matrix:

      Proc Rank   Global Row  Num Entries(Index,Value)
              0            0            2 (0, 2)  (1, -1)
              0            1            3 (0, -1)  (1, 2)  (2, -1)
              0            2            3 (1, -1)  (2, 2)  (3, -1)
              0            3            3 (2, -1)  (3, 2)  (4, -1)
              0            4            3 (3, -1)  (4, 2)  (5, -1)
              1            5            3 (5, 2)  (6, -1)  (4, -1)
              1            6            3 (5, -1)  (6, 2)  (7, -1)
              1            7            3 (6, -1)  (7, 2)  (8, -1)
              1            8            3 (7, -1)  (8, 2)  (9, -1)
              1            9            2 (8, -1)  (9, 2)

And here's the halo matrix with just the imported overlap rows:

      Proc Rank   Global Row  Num Entries(Index,Value)
              0            5            3 (4, -1)  (5, 2)  (6, -1)
              0            6            2 (5, -1)  (6, 2)
              1            4            3 (5, -1)  (4, 2)  (3, -1)
              1            3            2 (4, -1)  (3, 2)

Global row 6 on proc 0 doesn't have global column 7, and global row 3 on proc 1 doesn't have global column 2. So it is only possible to do two matvecs (not three) that agree with the standard SPMV that does an import at each step.

[jhux2]

Related to #6877

[jhux2]

I am wondering this could be related to issues discussed in #558.

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This issue was closed due to inactivity for 395 days.