[petsc-users] Solve Schur complement problem

[saturday luis]

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
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