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

[Danyang Su]

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. 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 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?

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 
> <mailto: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
>     <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/ <http://www.caam.rice.edu/%7Emk51/>

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