[petsc-users] BLOCK INVERSE FOR ILU

[Mark Adams]

It looks like it pivots in blocks and is a point-wise ILU:
https://urldefense.us/v3/__https://petsc.org/release/manualpages/PC/PCILU/__;!!G_uCfscf7eWS!d82xhlyQ6-cWmSO0PBI3pnGPDROVlCOPZn87hYtI4Pi9Kkbf4wgpQjnYsrJVy0pwHGtZYvPKXDxQCoq9BTvE6Ao$ 

Mark

On Wed, Jun 4, 2025 at 9:36 AM Frank Bramkamp <bramkamp at nsc.liu.se> wrote:

> Dear PETSc team,
>
> I have a general question regarding the implementation of the inverse
> For the ILU factorization.
>
> I am looking e.g. on the implementation for block size 6 for the BAIJ
> matrix format in serial:
> src/mat/impls/baij/seq/dgefa6.c
>
> I wonder:
> You are using pivoting in the inverse computation.
>
> But if one changes the position of elements or rows, do we not have to
> apply an inverse permutation at the end
> to get the inverse of the original matrix to some column ?!  Otherwise it
> is the inverse of the permutated matrix ?!
>
> I am not quite sure if one has to do this in principle or if my
> understanding is not quite correct.
> Maybe I miss something in your code.
>
>
> Thanks, Frank
>
>
>
>
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