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

[Matthew Knepley]

On Wed, May 24, 2017 at 12:50 PM, Danyang Su <danyang.su at gmail.com> wrote:

> Hi Matthew and Barry,
>
> Thanks for the quick response.
>
> I also tried superlu and mumps, both work but it is about four times
> slower than ILU(dt) prec through hypre, with 24 processors I have tested.
>
You mean the total time is 4x? And you are taking hundreds of iterates?
That seems hard to believe, unless you are dropping
a huge number of elements.

> When I look into the convergence information, the method using ILU(dt)
> still takes 200 to 3000 linear iterations for each newton iteration. One
> reason is this equation is hard to solve. As for the general cases, the
> same method works awesome and get very good speedup.
>
I do not understand what you mean here.

> I also doubt if I use hypre correctly for this case. Is there anyway to
> check this problem, or is it possible to increase the factorization level
> through hypre?
>
> I don't know.

  Matt

> Thanks,
>
> Danyang
>
> On 17-05-24 04:59 AM, Matthew Knepley wrote:
>
> 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/
>
>
>


-- 
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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