2009/9/11 tsjb00 <tsjb00 at hotmail.com> > Many thanks for your replies! I have three follow-up questions. I use the > AIJ format for the matrix, BCGS for KSP and ILU for PC. The matrix changes > with time. > > Now I put PC and KSP definition in initialization. In each timestep, I > redefine the matrix and rhs vector, use the KSPSetOperators and KSPSolve. > When I run the program, I get the following error info, which seems to occur > right before KSPSetOperators > [0]PETSC ERROR: --------------------- Error Message > ------------------------------------ > [0]PETSC ERROR: Arguments are incompatible! > [0]PETSC ERROR: Incompatible vector global lengths! > [0]PETSC ERROR: > ------------------------------------------------------------------------ > [0]PETSC ERROR: Petsc Release Version 3.0.0, Patch 5, Mon Apr 13 09:15:37 > CDT 2009 > [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: ../src_o_petsc/min3pp on a linux-gnu named pardiff by > jinbei Fri Sep 11 08:49:22 2009 > [0]PETSC ERROR: Libraries linked from > /home/jinbei/Soft/petsc-3.0.0-p5/linux-gnu-c-debug/lib > [0]PETSC ERROR: Configure run at Thu Aug 20 11:36:14 2009 > [0]PETSC ERROR: Configure options --with-cc=gcc --with-fc=ifort > --download-f-blas-lapack=1 --download-mpich=1 --with-shared=0 > [0]PETSC ERROR: > ------------------------------------------------------------------------ > [0]PETSC ERROR: VecCopy() line 1685 in src/vec/vec/interface/vector.c > [0]PETSC ERROR: KSPInitialResidual() line 60 in > src/ksp/ksp/interface/itres.c > [0]PETSC ERROR: KSPSolve_BCGS() line 44 in src/ksp/ksp/impls/bcgs/bcgs.c > [0]PETSC ERROR: KSPSolve() line 385 in src/ksp/ksp/interface/itfunc.c > > > What might cause the problem? >
You cannot change the problem size dynamically with KSP, since it allocates work vectors, etc. to support the computation. If the size changes, everything will have to be recreated. > Another question is, the BCGS+ILU combination is kind of slo w. Would you > please give me some suggestions on how to optimize the solver performance? > I've tried setting PC level to 1 and reducing maximum iterations, but > doesn't really work well. > Preconditioning is highly problem dependent. I do not believe in block-box preconditioners. > The last question is, if I want to use the true residual norm (based on > original A*x=y) and the norm of solution updates as the criteria of > convergence, what functions would do? Any example in the package I can refer > to? > http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/KSP/KSPSetNormType.html If you want something more sophisticated, you can always use http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/KSP/KSPSetConvergenceTest.html Matt > Many thanks again and have a nice day! > > > ------------------------------ > ??????????????? > ????????<http://www.microsoft.com/china/windows/windowslive/products/photos-share.aspx?tab=1> > -- 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 -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20090911/4cc0fe91/attachment.htm>
