[petsc-users] Can I use MAT_FINAL_ASSEMBLY instead of MAT_FLUSH_ASSEMBLY?

[Barry Smith]

On Nov 9, 2010, at 11:56 AM, Rongliang Chen wrote:

> Yes, I know. So this is why I need to use MAT_FINAL_ASSEMBLY instead of MAT_FLUSH_ASSEMBLY in the function MatAssemblyBegin/End when switching between ADD_VALUES and INSERT_VALUES in MatSetValues(). 
> But when I use the finally assembled matrix to multiply a vector using MatMult. I find that the output of  MatMult is wrong if I use multiprocessors.  So I doubt that the problem is come from "MAT_FINAL_ASSEMBLY instead of MAT_FLUSH_ASSEMBLY", but I am not sure. Thanks.

   Well the problem is either in your code or in PETSc. Send to petsc-maint at mcs.anl.gov a code that demonstrates the problem and we'll look into the problem.

   Barry

> 
> Regards,
> 
> Rongliang
> 
> On Tue, Nov 9, 2010 at 10:31 AM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> 
> On Nov 9, 2010, at 11:27 AM, Rongliang Chen wrote:
> 
> >    Message: 2
> > Date: Mon, 8 Nov 2010 19:57:16 -0600
> > From: Barry Smith <bsmith at mcs.anl.gov>
> > Subject: Re: [petsc-users] Can I use MAT_FINAL_ASSEMBLY instead of
> >        MAT_FLUSH_ASSEMBLY?
> > To: PETSc users list <petsc-users at mcs.anl.gov>
> > Message-ID: <52AFD8FB-17C1-4B51-97E9-C77112B69F3C at mcs.anl.gov>
> > Content-Type: text/plain; charset=us-ascii
> >
> >
> > On Nov 8, 2010, at 7:49 PM, Rongliang Chen wrote:
> >
> > > Hi everyone,
> > >
> > > Can I use MAT_FINAL_ASSEMBLY instead of MAT_FLUSH_ASSEMBLY in the function MatAssemblyBegin/End when switching between ADD_VALUES and INSERT_VALUES in MatSetValues()?  Thank you!
> > >
> > > Regards,
> > >
> > > Rongliang
> >
> > Yes, but generally there is no reason to. It is best to use the flush until your final assembly because then it doesn't do any work that needs to be redone or prematurely free memory that may be needed later.
> >
> > Why do you want to do that?
> >
> >   Barry
> >
> >
> >
> > Hi Barry,
> >
> > Thank you for your reply. I find that when I use MAT_FINAL_ASSEMBLY instead of MAT_FLUSH_ASSEMBLY in the function MatAssemblyBegin/End, it will
> >  cause problem. I do not know why.
> 
>   "cause problem" is not very helpful. What does that mean? Send all output to petsc-maint at mcs.anl.gov if it doesn't work.
> >
> > The reason that I want to use it like this is that I first set the matrix with ADD_VALUES and then I need to zero some rows of the matrix using MatZeroRowsLocalIS(), at last I still need to set some elements of the matrix with INSERT_VALUES. Between MatSetValues() and MatZeroRowsLocalIS() I need to use MAT_FINAL_ASSEMBLY.
> > The order is:
> > ADD_VALUES--->MatZeroRowsLocalIS()--->INSERT_VALUES.
> 
>  You need to use FINAL_ASSEMLY before the zero rows calls. Flush is not enough in that case.
> 
>   Barry
> 
> >
> > Thanks!
> >
> > Regards,
> >
> > Rongliang
> 
>