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
