[petsc-users] Solve Schur complement problem

[Smith, Barry F.]

  Luis,

   This doesn't really have any thing to do with the Schur complement per se, you are asking do an ILU on this abstract Schur complement matrix which is not possible.

   Almost for sure you want to use PCFIELDSPLIT and not directly create the MatCreateSchurComplement() yourself. PCFIELDSPLIT has many possible variants for solving systems with segregated Schur complement methods.

   Barry


> On Jan 23, 2018, at 1:13 PM, 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/documentation/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.
> 
> Thanks,
> 
> Luis