[petsc-users] Questions about MatConvert BAIJ to AIJ

[Barry Smith]

> On Mar 18, 2015, at 3:10 PM, Chung-Kan Huang <ckhuangf at gmail.com> wrote:
> 
> 
> 
> On Wed, Mar 18, 2015 at 2:54 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> 
>    You can use MatSetValuesBlocked() for AIJ matrices, obviously the matrix needs to have the block size
> 
> Barry,
> I don't think that is the problem.  The problem should be like Jed said, the MatConvert didn't actually work.  
> Now we can focus on how to make it work in my case.

   Just print the three matrices and confirm if they are different or the same.

> 
>   Barry
> 
> > On Mar 18, 2015, at 2:46 PM, Chung-Kan Huang <ckhuangf at gmail.com> wrote:
> >
> > Yes, I was suprised that I can still use MatSetValuesBlocked after I did MatConvert MATBAIJ to MATAIJ.
> >
> > Then I just found the mat type is still seqbaij which means the MatConvert didn't work.
> >
> > This is how I did MatConvert
> >
> > MatConvert(J, MATAIJ, MAT_REUSE_MATRIX, & J);
> >
> > where J is my Jacobian matrix.
> >
> > Thanks,
> >
> >
> > On Wed, Mar 18, 2015 at 2:24 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> >
> >   Are you always using MatSetValuesBlocked()?
> >
> >   Did you look at the three matrices (before passing to the solve), do they all have the exact same nonzero structure and entries?
> >
> >   Barry
> >
> > > On Mar 18, 2015, at 1:45 PM, Chung-Kan Huang <ckhuangf at gmail.com> wrote:
> > >
> > > So go back to my original question,
> > >
> > > I found the resuls look like
> > > MATBAIJ == MATBAIJ2MATAIJ != MATAIJ
> > > as I was expected to see
> > > MATBAIJ != MATBAIJ2MATAIJ == MATAIJ
> > >
> > > because I thought MATBAIJ2MATAIJ & MATAIJ should use the same ILU factorization.
> > >
> > > On Wed, Mar 18, 2015 at 1:33 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> > >
> > >    As I think I said earlier: ILU will behave differently with BAIJ and AIJ format. With BAIJ it uses a point block factorization (doing an ILU treating each block in the matrix as a single point (and doing a dense factorization for the inverse) while AIJ ignores the block size and just uses a point ILU. So in general the convergence with BAIJ vs AIJ and ILU will be different; usually BAIJ will converge better but it need not.
> > >
> > >    Barry
> > >
> > > > On Mar 18, 2015, at 1:23 PM, Chung-Kan Huang <ckhuangf at gmail.com> wrote:
> > > >
> > > > Sorry I didn't state my problem more accurate.  The entries in the input matrixes and vectors​ are correct -- they have right values and correct nonzero structure.
> > > > The KSP was setup so I can solve the lienar systems for an unsteady state convective problem.
> > > > I use KSPBCGS + PCILU and so far I only try sequential on a very small problem.
> > > > I wonder if blocked ilu is actually used in  MATBAIJ2MATAIJ case.
> > > >
> > > > Thanks,
> > > >
> > > >
> > >
> > >
> > >
> > >
> > > --
> > > Cheers
> > >
> >
> >
> >
> >
> > --
> > Cheers
> >
> 
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> 
> -- 
> Cheers
>