[petsc-users] Use of LSC preconditioning

[Alexander Lindsay]

Under what conditions can I use LSC preconditioning for field split
problems with Schur? Let's imagine that all I've done is called
SNESetJacobian with global A and P and provided the index sets for 0 and 1.
Based off of the documentation on the man page
https://petsc.org/release/docs/manualpages/PC/PCLSC/ it seems like I'd have
to do something more programmatically, e.g.

   PetscObjectCompose((PetscObject)Sp,"LSC_L",(PetscObject)L);
   PetscObjectCompose((PetscObject)Sp,"LSC_Lp",(PetscObject)Lp);

If I try to naively get LSC preconditioning from the command line without
doing something like the above, then I get SUBPC_ERROR. Is this to be
expected?

 0 Nonlinear |R| = 4.164062e-02
      0 Linear |R| = 4.164062e-02
  Linear solve did not converge due to DIVERGED_PC_FAILED iterations 0
                 PC failed due to SUBPC_ERROR
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