[petsc-users] AIJ vs BAIJ when using ILU factorization

[Fande Kong]

Thanks, Hong,

I will try the code with bs=1, and report back to you.

Fande,

On Tue, Mar 31, 2020 at 9:51 PM Zhang, Hong <hzhang at mcs.anl.gov> wrote:

> Fande,
> Checking aij.result:
> Mat Object: () 1 MPI processes
>           type: seqaij
>           rows=25816, cols=25816, bs=4
>           total: nonzeros=1297664, allocated nonzeros=1297664
>           total number of mallocs used during MatSetValues calls=0
>             using I-node routines: found 6454 nodes, limit used is 5
>
> i.e., it uses bs=4 with I-node. The implementation of MatSolve() is
> similar to baij with bs=4. What happens if you try aij with
> '-matload_block_size 1 -mat_no_inode true'?
> Hong
>
> ------------------------------
> *From:* petsc-users <petsc-users-bounces at mcs.anl.gov> on behalf of Fande
> Kong <fdkong.jd at gmail.com>
> *Sent:* Monday, March 30, 2020 12:25 PM
> *To:* PETSc users list <petsc-users at mcs.anl.gov>
> *Subject:* [petsc-users] AIJ vs BAIJ when using ILU factorization
>
> Hi All,
>
> There is a system of equations arising from the discretization of 3D
> incompressible Navier-Stoke equations using a finite element method. 4
> unknowns are placed on each mesh point, and then there is a 4x4 saddle
> point block on each mesh vertex.  I was thinking to solve the linear
> equations using an incomplete LU factorization (that will be eventually
> used as a subdomain solver for ASM).
>
> Right now, I am trying to study the ILU performance using AIJ and BAIJ,
> respectively. From my understanding, BAIJ should give me better results
> since it inverses the 4x4 blocks exactly, while AIJ does not. However, I
> found that both BAIJ and AIJ gave me identical results in terms of the
> number of iterations.  Was that just coincident?  Or in theory, they are
> just identical.  I understand the runtimes may be different because BAIJ
> has a better data locality.
>
>
> Please see the attached files for the results and solver configuration.
>
>
> Thanks,
>
> Fande,
>
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