[petsc-users] Question on incomplete factorization level and fill

[Matthew Knepley]

On Wed, May 24, 2017 at 2:21 AM, Danyang Su <danyang.su at gmail.com> wrote:

> Dear All,
>
> I use PCFactorSetLevels for ILU and PCFactorSetFill for other
> preconditioning in my code to help solve the problems that the default
> option is hard to solve. However, I found the latter one, PCFactorSetFill
> does not take effect for my problem. The matrices and rhs as well as the
> solutions are attached from the link below. I obtain the solution using
> hypre preconditioner and it takes 7 and 38 iterations for matrix 1 and
> matrix 2. However, if I use other preconditioner, the solver just failed at
> the first matrix. I have tested this matrix using the native sequential
> solver (not PETSc) with ILU preconditioning. If I set the incomplete
> factorization level to 0, this sequential solver will take more than 100
> iterations. If I increase the factorization level to 1 or more, it just
> takes several iterations. This remind me that the PC factor for this
> matrices should be increased. However, when I tried it in PETSc, it just
> does not work.
>
> Matrix and rhs can be obtained from the link below.
>
> https://eilinator.eos.ubc.ca:8443/index.php/s/CalUcq9CMeblk4R
>
> Would anyone help to check if you can make this work by increasing the PC
> factor level or fill?
>

We have ILU(k) supported in serial. However ILU(dt) which takes a tolerance
only works through Hypre

  http://www.mcs.anl.gov/petsc/documentation/linearsolvertable.html

I recommend you try SuperLU or MUMPS, which can both be downloaded
automatically by configure, and
do a full sparse LU.

  Thanks,

    Matt


> Thanks and regards,
>
> Danyang
>
>
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

http://www.caam.rice.edu/~mk51/
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