[petsc-users] Doubt in MPIPreallocation

[John Albequerque]

Barry,
I forgot to mention that the code is working fine with a single processor,
but when I increase the number of processors, as in this case 3 processors
have been used when the* error message was generated*. And yes, it has
something to do with the *off-diagonal* terms as I am increasing the number
of processes, the same error triggers for each row for which o_nnz[i] is
not zero.


Many thanks.

----
John Albequerque.

On Sat, Feb 20, 2016 at 2:38 AM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
>   You are setting nonzero preallocations for the "off diagonal" portion of
> the matrix, but one one process there is no off diagonal portion so you
> should be setting those values to all zero.
>
>   Barry
>
> > On Feb 19, 2016, at 2:29 PM, John Albequerque <johncfdcfd at gmail.com>
> wrote:
> >
> >
> > Dear Barry,
> > I am sorry I could not get you. I have also posted the entire error
> message so that you could get a deeper insight into it.
> >
> >
> > Many thanks.
> >
> > ----
> > John Albequerque.
> >
> ========================================================================================
> > Argument out of range
> > [0]PETSC ERROR: nnz cannot be greater than row length: local row 0 value
> 1 rowlength 0
> > [0]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html
> for trouble shooting.
> > [0]PETSC ERROR: Petsc Release Version 3.6.3, unknown
> > [0]PETSC ERROR: ./MatSparse on a linux-gnu-c-debug named John by johncfd
> Sat Feb 20 01:36:01 2016
> > [0]PETSC ERROR: Configure options --with-cc=gcc --with-cxx=g++
> --with-fc=gfortran --download-fblaslapack --download-mpich
> > [0]PETSC ERROR: #1 MatSeqAIJSetPreallocation_SeqAIJ() line 3567 in
> /home//MyStuff/ClonedRepos/petsc/src/mat/impls/aij/seq/aij.c
> > [0]PETSC ERROR: #2 MatSeqAIJSetPreallocation() line 3539 in
> /home/MyStuff/ClonedRepos/petsc/src/mat/impls/aij/seq/aij.c
> > [0]PETSC ERROR: #3 MatMPIAIJSetPreallocation_MPIAIJ() line 2835 in
> /home/MyStuff/ClonedRepos/petsc/src/mat/impls/aij/mpi/mpiaij.c
> > [0]PETSC ERROR: #4 MatMPIAIJSetPreallocation() line 3532 in
> /home/MyStuff/ClonedRepos/petsc/src/mat/impls/aij/mpi/mpiaij.c
> >
> =========================================================================================
> >
> >
> > On Sat, Feb 20, 2016 at 12:35 AM, Barry Smith <bsmith at mcs.anl.gov>
> wrote:
> >
> > > On Feb 19, 2016, at 12:54 PM, John Albequerque <johncfdcfd at gmail.com>
> wrote:
> > >
> > > Jed, one more
> > >
> > > nnz cannot be greater than row length: local row 0 value 1 rowlength 0
> >
> >   Always send the entire error message, this provides the context to
> know what the hey is going on.
> >
> >   It looks like you set a matrix block (if you are using an MPI matrix
> on one process this could the the "off-diagonal" block)  which has no
> columns (hence row length is zero) but you claim you need to preallocate an
> entry (the 1).
> >
> >   Barry
> >
> > >
> > > How do I deal with this error?
> > >
> > > Thanks.
> > >
> > > ----
> > > John Albequerque.
> > >
> > >
> > >
> > > On Fri, Feb 19, 2016 at 8:17 PM, John Albequerque <
> johncfdcfd at gmail.com> wrote:
> > > Thank you very much, I will try it.
> > >
> > >
> > > Thanks
> > >
> > > ----
> > > John Albequerque.
> > >
> > >
> > >
> > > On Fri, Feb 19, 2016 at 8:16 PM, Jed Brown <jed at jedbrown.org> wrote:
> > > John Albequerque <johncfdcfd at gmail.com> writes:
> > >
> > > > So Jed, what you are suggesting is that I should set only the
> non-zero
> > > > elements while using
> > > > *  MatSetValues(A,(high-low),**idxm,nc,idxn,values,INSERT_*
> > > >
> > > > *VALUES);*
> > > > And not mention the zero elements and for that I should loop over
> all local
> > > > rows and then set each of the value.
> > >
> > > Yes.  The whole point of a sparse matrix is to spend no time or storage
> > > on 0.0 entries.  If you allocate a dense matrix and store all the
> zeros,
> > > you're just being inefficient relative to a dense format.
> > >
> > >
> >
> >
>
>
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