symmetric reordering and incomplete factorization with tolerance?

[Barry Smith]

    You should use rcm+icc if you want to keep a symmetric  
preconditioner.

    Depending on your matrix you might want to use KSPCR or KSPMINRES  
or even KSPSYMMLQ
instead of bicgstab?

    We don't have a drop tolerance ICC and I do not recommend our drop  
tolerance ILU.

    Barry


On Sep 16, 2008, at 10:23 AM, zhifeng sheng wrote:

> Dear all
>
> I used the reordering scheme in petsc, and I would like to know  
> whether they are symmetric or not.
>
> I have a symmetric matrix (for 3D system) and I tried to solve it  
> with petsc and with matlab.
>
> In petsc I used rcm + ILU + bicgstab. while in matlab I used symrcm 
> +ICC+bicgstab.
>
> it seems that with symmetric reordering, the factorization is  
> somewhat faster... So I am wondering if it is possible to apply a  
> symmetric reordering?
>
> PS: in Matlab, an incomplete factorization can be done with a  
> tolerance (e.g. ICC(1e-4) ), can I do something like that with Petsc?
>
> Thanks a lot
> Best regards
> Zhifeng Sheng
>
>