[petsc-users] incomplete cholesky with a drop tolerance

[Jed Brown]

On Sun, Jul 22, 2012 at 9:49 AM, Umut Tabak <u.tabak at tudelft.nl> wrote:

> Dear all,
>
> I am testing some iterative methods with MATLAB and aside with PETSc
> however I have a question which might be answered in the documentation
> however I could not find that?
>
> In MATLAB, at least on recent versions, one can specify a drop tolerance
> for the incomplete cholesky preconditioner, I was wondering if the same is
> possible with PETSc or not?
>

You can get an ILUT using MatSuperluSetILUDropTol
(-mat_superlu_ilu_droptol) or from Hypre's PILUT (-pc_hypre_pilut_tol).


> One more question, is the condition number order 1e+6(estimated with
> condest in MATLAB) rather high for an iterative method? With icc, with a
> drop tolerance of 1e-3 or 1e-4, as a preconditioner to pcg, I can get
> decent iteration numbers to convergence in MATLAB, it is sometimes even
> faster than solving the system with the available factorization information
> and I was wondering if I can make it faster with some other options in
> PETSc or not?
>

What continuum equations are you solving? What discretization?
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