[petsc-users] Error using the same ksp with different operator sizes

[Eloy Romero]

Dear all,

I have a code that using the same ksp, solves some matrices with 
different size in that way:

   ierr = KSPCreate(PETSC_COMM_WORLD, &ksp);
   ...
   ierr = KSPSetOperators(ksp, A, A, DIFFERENT_NONZERO_PATTERN); 
CHKERRQ(ierr);
   ierr = KSPSolve(ksp, v0, v1); CHKERRQ(ierr);
   ...
   ierr = KSPSetOperators(ksp, B, B, DIFFERENT_NONZERO_PATTERN); 
CHKERRQ(ierr);
   ierr = KSPSolve(ksp, w0, w1); CHKERRQ(ierr);
   ...

The KSPSolve is called with vectors of appropriated length. However I 
obtain the following error in the second call to KSPSolve:

[0]PETSC ERROR: --------------------- Error Message 
------------------------------------
[0]PETSC ERROR: Nonconforming object sizes!
[0]PETSC ERROR: Mat mat,Vec x: global dim 1083 66!
[0]PETSC ERROR: 
------------------------------------------------------------------------
[0]PETSC ERROR: Petsc Release Version 3.1.0, Patch 0, unknown
[0]PETSC ERROR: See docs/changes/index.html for recent updates.
[0]PETSC ERROR: See docs/faq.html for hints about trouble shooting.
[0]PETSC ERROR: See docs/index.html for manual pages.
[0]PETSC ERROR: 
------------------------------------------------------------------------
[0]PETSC ERROR: ./veccomp_ex2 on a linux-gnu named yah by eloy Thu May 
13 11:27:31 2010
[0]PETSC ERROR: Libraries linked from 
/usr/src/petsc-release-3.1/linux-gnu-c-debug/lib
[0]PETSC ERROR: Configure run at Wed Mar 31 13:34:33 2010
[0]PETSC ERROR: Configure options --with-blas-lapack-dir="[/usr/lib]" 
--with-clanguage=C --with-shared=0 --with-mpi=1 --with-cc=mpicc 
--with-cxx=mpicxx --download-hypre=ifneeded --with-hypre=1 
--with-fc=mpif90 --with-mumps --download-mumps=ifneeded 
--download-blacs=ifneeded --download-scalapack=ifneeded 
--download-parmetis=ifneeded --download-superlu_dist=ifneeded 
--with-superlu_dist --with-ml --download-ml=ifneeded --with-mpi-dir=/usr
[0]PETSC ERROR: 
------------------------------------------------------------------------
[0]PETSC ERROR: MatMult() line 1889 in src/mat/interface/matrix.c
[0]PETSC ERROR: PCApplyBAorAB() line 585 in src/ksp/pc/interface/precon.c
[0]PETSC ERROR: GMREScycle() line 161 in src/ksp/ksp/impls/gmres/gmres.c
[0]PETSC ERROR: KSPSolve_GMRES() line 241 in src/ksp/ksp/impls/gmres/gmres.c
[0]PETSC ERROR: KSPSolve() line 396 in src/ksp/ksp/interface/itfunc.c
[0]PETSC ERROR: main() line 59 in veccomp_ex2.c

I don't find in the reference that one can or cannot use the ksp with 
matrices of different size, so I don't know if it is really a bug.

In my application, a ksp configured by the user is given, and I would 
like to use that configuration for solving all the linear systems. 
Creating new ksps and configuring them with KSPSetFromOptions is not a 
complete solution because the user could modify the ksp by code.