[petsc-users] Incomplete Cholesky Factorization in petsc

[Wenlong Gong]

Barry, Thank you for the reply! It makes sense If two IC() function returns
slightly different factored matrix. But the IC factor matrix from PETSc is
not even close to what I get from ichol in Matlab.
Ultimately I need this incomplete cholesky factorization function wrapped
in R once it gives correct result. Not sure if I used the easiest way to
get IC so I also seek for help on getting a concise version of IC().

-Wendy


On Mon, Dec 4, 2017 at 10:07 PM, Smith, Barry F. <bsmith at mcs.anl.gov> wrote:

>
>   I'm not sure what your goal is. In general two different IC(0) codes
> might produce slightly different factorizations based on implementation
> details even if they claim to run the same algorithm so I don't think there
> is a reason to try to compare the factors they produce.
>
>   In addition PETSc, as well as most IC/ILU/LU  codes store the factored
> matrices in a "non-conventional" form that is optimized for performance so
> it is not easy to just pull out the "factors" to look at them or compare
> them.
>
>     Barry
>
>
> > On Dec 4, 2017, at 9:07 PM, Wenlong Gong <wenlonggong at gmail.com> wrote:
> >
> > Hello,
> >
> > I'm trying to use the Incomplete Cholesky Factorization for a sparse
> matrix in petsc. I started with a 10*10 matrix and used ksp and pc in order
> to get the ICC(0) factor, with no fill-in, natural ordering. However, the
> returned factor matrix does not match with the answer I got from matlab
> ichol() function.
> >
> > The code with the hard-coded data is attached here. I would appreciate
> if anyone could help check if I did anything wrong.Please let me know if
> there is easier way to get this incomplete cholesky factor. Thanks!
> >
> > Best regards,
> > Wendy
> >
> > <repex.c>
>
>
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