[petsc-users] Questions about MatConvert BAIJ to AIJ

[Barry Smith]

  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
>