[petsc-users] PCFIELDSPLIT question

Tue Feb 2 14:35:34 CST 2016

Thank you so much Matt.

I now tried the following:

======================================================
call KSPCreate(PETSC_COMM_WORLD,ksp,ierr)
call KSPGetPC(ksp,pc,ierr)

call PCFieldSplitSetIS(pc,"0",gdofu_is,ierr);
call ISDestroy(gdofu_is,ierr)
call PCFieldSplitSetIS(pc,"1",gdofchi_is,ierr);
call ISDestroy(gdofchi_is,ierr)
call PCFieldSplitSetIS(pc,"2",gdofp_is,ierr);
call ISDestroy(gdofp_is,ierr)
call PCFieldSplitSetIS(pc,"3",gdofphi_is,ierr);
call ISDestroy(gdofphi_is,ierr)

! Amat changes in each time steps
call KSPSetOperators(ksp,Amat,Amat,ierr) !version >= 3.5.0

call KSPSolve(ksp,bvec,xvec,ierr)
======================================================

But I get the following error:

[0]PETSC ERROR: --------------------- Error Message
--------------------------------------------------------------
[0]PETSC ERROR: Petsc has generated inconsistent data
[0]PETSC ERROR: Unhandled case, must have at least two fields, not 1
[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, Dec, 03, 2015
[0]PETSC ERROR:
/tigress/hgharti/gitwork/SPECFEM3D_GLOBEVSPP/./bin/xspecfem3D on a
arch-linux2-c-debug named tiger-r3c1n7 by hgharti Tue Feb  2 15:
29:30 2016
[0]PETSC ERROR: Configure options
--with-blas-lapack-dir=/opt/intel/composer_xe_2015.2.164/mkl/lib/intel64/
--with-cc=mpicc --with-cxx=mpicxx --wit
h-fc=mpif90 --with-mpiexec=mpiexec --with-debugging=1
--download-scalapack --download-mumps --download-pastix
--download-superlu --download-superlu_dist --download-metis
--download-parmetis --download-ptscotch --download-hypre
[0]PETSC ERROR: #1 PCFieldSplitSetDefaults() line 469 in
/home/hgharti/lsoft/petsc-3.6.3-intel16-mpi5/src/ksp/pc/impls/fieldsplit/fieldsplit.c
[0]PETSC ERROR: #2 PCSetUp_FieldSplit() line 486 in
/home/hgharti/lsoft/petsc-3.6.3-intel16-mpi5/src/ksp/pc/impls/fieldsplit/fieldsplit.c
[0]PETSC ERROR: #3 PCSetUp() line 983 in
/home/hgharti/lsoft/petsc-3.6.3-intel16-mpi5/src/ksp/pc/interface/precon.c
[0]PETSC ERROR: #4 KSPSetUp() line 332 in
/home/hgharti/lsoft/petsc-3.6.3-intel16-mpi5/src/ksp/ksp/interface/itfunc.c
[0]PETSC ERROR: #5 KSPSolve() line 546 in
/home/hgharti/lsoft/petsc-3.6.3-intel16-mpi5/src/ksp/ksp/interface/itfunc.c
forrtl: error (76): Abort trap signal

Am I missing something?

Thanks,
Hom Nath

On Tue, Feb 2, 2016 at 3:24 PM, Matthew Knepley <knepley at gmail.com> wrote:
> On Tue, Feb 2, 2016 at 2:20 PM, Hom Nath Gharti <hng.email at gmail.com> wrote:
>>
>> Hi Matt, hi all,
>>
>> I am trying to use PCFIELDSPLIT for my solver which consists of 4
>> different variables, namely, u (displacement vector), \chi
>> (displacement potential), p(pressure), and \phi (gravity potential).
>>
>> My code segment looks like the following:
>> ======================================================
>> call KSPCreate(PETSC_COMM_WORLD,ksp,ierr)
>> call KSPGetPC(ksp,pc,ierr)
>> nsplit=4
>> call PCFieldSplitSetBlockSize(pc,nsplit,ierr);
>
>
> You do not need the statement above.
>
>>
>> call PCFieldSplitSetIS(pc,"0",gdofu_is,ierr);
>> call ISDestroy(gdofu_is,ierr)
>> call PCFieldSplitSetIS(pc,"1",gdofchi_is,ierr);
>> call ISDestroy(gdofchi_is,ierr)
>> call PCFieldSplitSetIS(pc,"2",gdofp_is,ierr);
>> call ISDestroy(gdofp_is,ierr)
>> call PCFieldSplitSetIS(pc,"3",gdofphi_is,ierr);
>> call ISDestroy(gdofphi_is,ierr)
>>
>> call PCFieldSplitGetSubKSP(pc,nsplit,subksp,ierr);
>
>
> These SetOperators() calls are wrong. I am not sure why you want them here.
> Also, that means you do not need the call above.
>
>   Thanks,
>
>      Matt
>
>>
>> call KSPSetOperators(subksp(1),Amat,Amat,ierr);
>> call KSPSetOperators(subksp(2),Amat,Amat,ierr);
>> call KSPSetOperators(subksp(3),Amat,Amat,ierr);
>> call KSPSetOperators(subksp(4),Amat,Amat,ierr);
>>
>> call KSPSolve(ksp,bvec,xvec,ierr)
>> ======================================================
>>
>> But I am getting the following error:
>> [79]PETSC ERROR: Null argument, when expecting valid pointer
>> [79]PETSC ERROR: Null Object: Parameter # 1
>> [79]PETSC ERROR: #1 KSPSetOperators() line 536 in
>> /home/hgharti/lsoft/petsc-3.6.3-intel16-mpi5/src/ksp/ksp/interf
>>
>> It looks like I am doing something wrong in "call KSPSetOperators" but
>> I could not figure that out.
>>
>> Could anybody help me to fix this problem? I looked into almost all
>> related examples but I could not really figure out the correct steps
>> after "call PCFieldSplitSetIS".
>>
>> Any help will be greatly appreciated.
>>
>> Best,
>> Hom nath
>>
>> On Sun, Jan 24, 2016 at 7:14 PM, Hom Nath Gharti <hng.email at gmail.com>
>> wrote:
>> > Thank you so much Matt! I will try.
>> >
>> > Hom Nath
>> >
>> > On Sun, Jan 24, 2016 at 6:26 AM, Matthew Knepley <knepley at gmail.com>
>> > wrote:
>> >> On Fri, Jan 22, 2016 at 2:19 PM, Hom Nath Gharti <hng.email at gmail.com>
>> >> wrote:
>> >>>
>> >>> Dear all,
>> >>>
>> >>> I am new to PcFieldSplit.
>> >>>
>> >>> I have a matrix formed using MATMPIAIJ. Is it possible to use
>> >>> PCFIELDSPLIT operations in this type of matrix? Or does it have to be
>> >>> MATMPIBIJ or MATNEST format?
>> >>
>> >>
>> >> Yes, you can split AIJ.
>> >>
>> >>>
>> >>> If possible for MATMPIAIJ, could anybody provide me a simple example
>> >>> or few steps? Variables in the equations are displacement vector,
>> >>> scalar potential and pressure.
>> >>
>> >>
>> >> If you do not have a collocated discretization, then you have to use
>> >>
>> >>
>> >>
>> >> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/PC/PCFieldSplitSetIS.html
>> >>
>> >>   Thanks,
>> >>
>> >>      Matt
>> >>
>> >>>
>> >>> Thanks for help.
>> >>>
>> >>> Hom Nath
>> >>
>> >>
>> >>
>> >>
>> >> --
>> >> What most experimenters take for granted before they begin their
>> >> experiments
>> >> is infinitely more interesting than any results to which their
>> >> experiments
>> >> lead.
>> >> -- Norbert Wiener
>
>
>
>
> --
> What most experimenters take for granted before they begin their experiments
> is infinitely more interesting than any results to which their experiments
> lead.
> -- Norbert Wiener