I've check it in Matlab. the matrix A is symmetric and has no negative eigenvalues( only a zero eigen value). I've also checked that the nullspace is correct( norm(A*phi)<1e-11); Thanks.
On Wed, Nov 23, 2011 at 1:26 PM, Barry Smith <bsmith at mcs.anl.gov> wrote: > > Print out the matrix for a small grid then check in Matlab that it is > symmetric and has no negative eigenvalues. > > Barry > > > On Nov 23, 2011, at 9:50 AM, Shiyuan wrote: > > > Hi, > > I want to solve a singular system with a known nullspace. However, I > the KSP solve diverges with KSP_INDEFINTE_PC even if I disable the > preconditioning by PCNONE. > > this is how I setup the system. What did I do wrong? Any possible > causes? Thanks. > > > > > > ierr=MatNullSpaceCreate(PETSC_COMM_SELF,PETSC_FALSE,1,&phi,&nsp);CHKERRV(ierr); > > ierr=KSPCreate(PETSC_COMM_SELF,&ksp);CHKERRV(ierr); > > ierr=KSPSetOperators(ksp,A,A,DIFFERENT_NONZERO_PATTERN);CHKERRV(ierr); > > ierr=KSPSetNullSpace(ksp,nsp);CHKERRV(ierr); > > ierr=KSPSetType(ksp,KSPCG);CHKERRV(ierr); > > ierr=KSPGetPC(ksp,&prec);CHKERRV(ierr); > > ierr=PCSetType(prec,PCNONE);CHKERRV(ierr); > > ierr=KSPSetTolerances(ksp,1e-5,1e-20,1e5,10000);CHKERRV(ierr); > > ierr=KSPSetFromOptions(ksp);CHKERRV(ierr); > > ierr=KSPSetUp(ksp);CHKERRV(ierr); > > > > Shiyuan > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20111123/940092a4/attachment.htm>
