dolfin team mailing list archive

[Andre Massing <massing@xxxxxxxxx>]

Anders Logg wrote:
> On Fri, Apr 23, 2010 at 10:44:19AM +0100, Garth N. Wells wrote:
> > Anders Logg wrote:
> > > On Fri, Apr 23, 2010 at 09:34:16AM +0100, Garth N. Wells wrote:
> > > > This sounds very PETSc-speecific. Should it be a parameter of
> > > > PETScMatrix only?
> > > >
> > > > Garth
> > > Yes, perhaps. I find it a bit strange that MatZeroRows breaks for
> > > rows without elements.
> > Send a PETSc bug report?
>
> Yes, that might be the best option.
>
> > A solution would be to check the number of row entries, if possible.
>
> I also though of that but didn't find a fast way to check it. Perhaps
> I've overlooked some PETSc function that does this?

I checked the PETSc doc and the DOLFIN code and and setting the 
parameter in dolfin/la/PETScMatrix.cpp

MatSetOption(*A, MAT_KEEP_ZEROED_ROWS, PETSC_TRUE);

causes to the MatZeroRowIS function not to the change the nonzero structure:
http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/Mat/MatSetOption.html#MatSetOption
and
http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/Mat/MatZeroRowsIS.html#MatZeroRowsIS

and seems therefore (in our case) to throw an error if you want to add a 
nonzero value to a zero diagonal entry.

Just tested it here and it went fine without setting use_ident=false.
What is the reason for setting this option?

--
Andre
> --
> Anders
>
>
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