[petsc-users] How to define blocks for PCFIELDSPLIT?

[Barry Smith]

  The error is in PCFieldSplitSetDefaults() so it is seemingly ignoring your calls to PCFieldSplitSetIS() 
make sure those calls come AFTER your call to KSPSetFromOptions() in your code.

  Barry

> On Mar 6, 2017, at 5:05 PM, Lucas Clemente Vella <lvella at gmail.com> wrote:
> 
> I tried to split my matrix (attached drawing of the non-null elements) by calling PCFieldSplitSetIS() twice:
> 
> PCFieldSplitSetIS(pc, "p", zero_to_n);
> PCFieldSplitSetIS(pc, "u", n_to_m);
> 
> But upon running with options:
> 
> -ksp_type preonly -pc_type fieldsplit
> 
> 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 3.7.3, Jul, 24, 2016 
> [0]PETSC ERROR: /home/lvella/src/higtree/examples/read-amr-solve-ns-cfl-example-2d on a x86_64-linux-gnu-real named lvella-workstation by lvella Mon Mar  6 20:01:47 2017
> [0]PETSC ERROR: Configure options --build=x86_64-linux-gnu --prefix=/usr --includedir=${prefix}/include --mandir=${prefix}/share/man --infodir=${prefix}/share/info --sysconfdir=/etc --localstatedir=/var --with-silent-rules=0 --libdir=${prefix}/lib/x86_64-linux-gnu --libexecdir=${prefix}/lib/x86_64-linux-gnu --with-maintainer-mode=0 --with-dependency-tracking=0 --with-debugging=0 --shared-library-extension=_real --with-hypre=1 --with-hypre-dir=/usr --with-clanguage=C++ --with-shared-libraries --with-pic=1 --useThreads=0 --with-fortran-interfaces=1 --with-mpi-dir=/usr/lib/openmpi --with-blas-lib=-lblas --with-lapack-lib=-llapack --with-blacs=1 --with-blacs-lib="-lblacsCinit-openmpi -lblacs-openmpi" --with-scalapack=1 --with-scalapack-lib=-lscalapack-openmpi --with-mumps=1 --with-mumps-include="[]" --with-mumps-lib="-ldmumps -lzmumps -lsmumps -lcmumps -lmumps_common -lpord" --with-suitesparse=1 --with-suitesparse-include=/usr/include/suitesparse --with-suitesparse-lib="-lumfpack -lamd -lcholmod -lklu" --with-spooles=1 --with-spooles-include=/usr/include/spooles --with-spooles-lib=-lspooles --with-ptscotch=1 --with-ptscotch-include=/usr/include/scotch --with-ptscotch-lib="-lptesmumps -lptscotch -lptscotcherr" --with-fftw=1 --with-fftw-include="[]" --with-fftw-lib="-lfftw3 -lfftw3_mpi" --with-superlu=0 --CXX_LINKER_FLAGS=-Wl,--no-as-needed --prefix=/usr/lib/petscdir/3.7.3/x86_64-linux-gnu-real PETSC_DIR=/build/petsc-fA70UI/petsc-3.7.3.dfsg1 --PETSC_ARCH=x86_64-linux-gnu-real CFLAGS="-g -O2 -fdebug-prefix-map=/build/petsc-fA70UI/petsc-3.7.3.dfsg1=. -fstack-protector-strong -Wformat -Werror=format-security -fPIC" CXXFLAGS="-g -O2 -fdebug-prefix-map=/build/petsc-fA70UI/petsc-3.7.3.dfsg1=. -fstack-protector-strong -Wformat -Werror=format-security -fPIC" FCFLAGS="-g -O2 -fdebug-prefix-map=/build/petsc-fA70UI/petsc-3.7.3.dfsg1=. -fstack-protector-strong -fPIC" FFLAGS="-g -O2 -fdebug-prefix-map=/build/petsc-fA70UI/petsc-3.7.3.dfsg1=. -fstack-protector-strong -fPIC" CPPFLAGS="-Wdate-time -D_FORTIFY_SOURCE=2" LDFLAGS="-Wl,-Bsymbolic-functions -Wl,-z,relro -fPIC" MAKEFLAGS=w
> [0]PETSC ERROR: #1 PCFieldSplitSetDefaults() line 474 in /build/petsc-fA70UI/petsc-3.7.3.dfsg1/src/ksp/pc/impls/fieldsplit/fieldsplit.c
> [0]PETSC ERROR: #2 PCSetUp_FieldSplit() line 491 in /build/petsc-fA70UI/petsc-3.7.3.dfsg1/src/ksp/pc/impls/fieldsplit/fieldsplit.c
> [0]PETSC ERROR: #3 PCSetUp() line 968 in /build/petsc-fA70UI/petsc-3.7.3.dfsg1/src/ksp/pc/interface/precon.c
> [0]PETSC ERROR: #4 KSPSetUp() line 390 in /build/petsc-fA70UI/petsc-3.7.3.dfsg1/src/ksp/ksp/interface/itfunc.c
> [0]PETSC ERROR: #5 KSPSolve() line 599 in /build/petsc-fA70UI/petsc-3.7.3.dfsg1/src/ksp/ksp/interface/itfunc.c
> 
> What is the proper way to setup PCFIELDSPLIT in this case?
> 
> 
> 2017-03-01 16:26 GMT-03:00 Barry Smith <bsmith at mcs.anl.gov>:
> 
> > On Mar 1, 2017, at 12:59 PM, Lucas Clemente Vella <lvella at gmail.com> wrote:
> >
> > I have a parallel AIJ matrix and I know exactly which element belongs to each one of the 4 submatrices blocks I want to use to solve the linear system. The blocks are not strided, because they have different number of elements.
> >
> > I understand that I must use PCFieldSplitSetIS(), since PCFieldSplitSetFields() is only for strided blocks. What I don't understand is how to create the IS structure I must pass to it.
> >
> > Each matrix coefficient is identified by a pair (i, j), but on IS creation functions, like ISCreateGeneral() and ISCreateBlock(), I am supposed to provide a one dimension set of indices. How does these indices relates to the matrix coefficients?
> 
>    PCFieldSplitSetIS() always indicates SQUARE blocks along the diagonal of the original matrix. Hence you need only one IS to define a block, you don't need one for the columns and one for the rows.  The IS is telling what rows AND columns you want in the block.
> 
> 
> > Also, ISCreateGeneral() seems to create a single block, and ISCreateBlock() seems to create multiple blocks of the same size.
> 
>     ISCreateBlock() does not create multi blocks, it creates a single IS that has "block structure", for example 0,1, 3, 4, 6, 7, 9,10, ....
> > How to create multiple blocks with different sizes?
> 
>    ISCreateGeneral().
> 
> 
> >
> > Thanks.
> >
> > --
> > Lucas Clemente Vella
> > lvella at gmail.com
> 
> 
> 
> 
> -- 
> Lucas Clemente Vella
> lvella at gmail.com
> <matrix.png>