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

[Danyang Su]

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?

Thanks and regards,

Danyang