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

[Barry Smith]

> On 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.

   SetFill doesn't affect the numerical answers at all. It is just a prediction you make of how much memory you expect to be used inside the factorization.


> 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?
> 
> Thanks and regards,
> 
> Danyang
> 
>