[petsc-users] KSP with MatNullSpace

[Shiyuan]

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
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