[petsc-users] Solve Schur complement problem

[saturday luis]

Great! This is exactly what I want.

Thanks!

Luis

2018-01-23 12:27 GMT-08:00 Matthew Knepley <knepley at gmail.com>:

> On Wed, Jan 24, 2018 at 6:13 AM, saturday luis <luis.saturday at gmail.com>
> wrote:
>
>> Hi PETSc team:
>>
>> I am trying to solve a Stokes problem in a segregated manner, in which
>> the pressure field is obtained by solving the pressure Schur complement.
>> This is what I did.
>>
>> I created a Schur complement by calling
>>
>> Mat S;
>> MatCreateSchurComplement(gloAssem_ptr->K_11, gloAssem_ptr->K_11,
>> gloAssem_ptr->K_10, gloAssem_ptr->K_01, gloAssem_ptr->K_00, &S);
>>
>> Then I use the Mat S as an input for KSP:
>> KSPSetOperators(ksp, S, S);
>>
>> I got error message as follows.
>> [0]PETSC ERROR: See http://www.mcs.anl.gov/petsc/d
>> ocumentation/linearsolvertable.html for possible LU and Cholesky solvers
>> [0]PETSC ERROR: Could not locate a solver package. Perhaps you must
>> ./configure with --download-<package>
>> [0]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html
>> for trouble shooting.
>> [0]PETSC ERROR: Petsc Release Version 3.8.3, Dec, 09, 2017
>> [0]PETSC ERROR: ./bipn3d on a arch-linux2-cxx-debug named bacon by luis
>> Tue Jan 23 11:02:34 2018
>> [0]PETSC ERROR: Configure options --prefix=~/lib/petsc-3.8.3-debug
>> --with-x=0 -with-pic --with-mpi-compilers=1 --with-mpi-dir=/home/lib/mpich-3.2/
>> --with-clanguage=C++ --with-scalar-type=real --with-shared-libraries=1
>> --with-precision=double --with-hypre=1 --download-hypre --with-spai=1
>> --download-spai --with-superlu_dist=1 --download-superlu_dist
>> --with-superlu=1 --download-superlu --with-parmetis=1 --download-parmetis
>> --with-metis=1 --download-metis --with-mumps=1 --download-mumps
>> --with-parmetis=1 --download-parmetis --with-metis=1 --download-metis
>> --with-scalapack=1 --download-scalapack --with-blacs=1 --download-blacs
>> --with-spooles=1 --download-spooles --with-debugging=yes
>> --download-fblaslapack
>> [0]PETSC ERROR: #1 MatGetFactor() line 4346 in
>> /home/lib/petsc-3.8.3/src/mat/interface/matrix.c
>> [0]PETSC ERROR: #2 PCSetUp_ILU() line 142 in
>> /home/lib/petsc-3.8.3/src/ksp/pc/impls/factor/ilu/ilu.c
>> [0]PETSC ERROR: #3 PCSetUp() line 924 in /home/lib/petsc-3.8.3/src/ksp/
>> pc/interface/precon.c
>> [0]PETSC ERROR: #4 KSPSetUp() line 381 in /home/lib/petsc-3.8.3/src/ksp/
>> ksp/interface/itfunc.c
>> [0]PETSC ERROR: #5 KSPSolve() line 612 in /home/lib/petsc-3.8.3/src/ksp/
>> ksp/interface/itfunc.c
>>
>> Let me know if you can see any issue in the usage of Schur complement
>> creation.
>>
>
> This will work if you give
>
>   -pc_type none
>
> which will give you plain GMRES. As Barry says, a more sophisticated thing
> to do is to use PCFIELDSPLIT. I do this in the examples for SNES ex62.
>
>   Thanks,
>
>      Matt
>
>
>> Thanks,
>>
>> Luis
>>
>
>
>
> --
> 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
>
> https://www.cse.buffalo.edu/~knepley/ <http://www.caam.rice.edu/~mk51/>
>
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