[petsc-users] incomplete cholesky with a drop tolerance

[Umut Tabak]

On 07/22/2012 05:14 PM, Jed Brown wrote:
> On Sun, Jul 22, 2012 at 9:49 AM, Umut Tabak <u.tabak at tudelft.nl 
> <mailto: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)..
Dear Jed Thanks for this tip, I will try...
>
>
>     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?
Helmholtz equation, 3d discretization of a fluid domain, basically the 
operator is singular however for my problem I can delete one of the rows 
of the matrix, for this case, I  and get a non-singular operator that I 
can continue my operations, basically, I am getting a matrix with size 
n-1, where original problem size is n. However, this application is 
pretty problem specific, then I can use this full-rank matrix in linear 
solutions. The condition number estimate belongs to this full-rank 
matrix that is extracted from the original singular operator...

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120722/6ba485a3/attachment-0001.html>