[petsc-users] Preconditioner for LSC

[Jed Brown]

If you've already attached a MatShell, you could presumably use -fieldsplit_1_lsc_pc_type mat to just call its MatMult.

The sense I've gotten when I wrote PCLSC and was experimenting with these methods is that the main selling point of LSC (for most discretizations) is that it's more algebraic than the cheaper PCD methods.

Elena Travaglia <elena.travaglia at edu.unito.it> writes:

> Dear PETSc users,
>
> we would like to compare our preconditioner for the Schur complement
> of a Stokes system, with the LSC preconditioner already implemented in
> PETSc. Following the example in the PETSc manual, we've tried
>    -fieldsplit_1_pc_type lsc -fieldsplit_1_lsc_pc_type ml
> but this is not working (properly) on our problem.
>
> On the other hand we think we have a good preconditioner for A10*A01,
> so  we'd like to try
>    -fieldsplit_1_pc_type lsc -fieldsplit_1_lsc_pc_type shell
> but we cannot figure out how to attach our apply() routine to
> the pc object of fieldsplit_1_lsc.
>
> Can this be done in the current interface?
> Or perhaps, should we call KSPGetOperators on the fieldsplit_1 solver
> and attach to its Sp operator a "LSC_Lp" of type MATSHELL with our routine
> attached to the MATOP_SOLVE of the shell matrix?
>
> Thanks in advance,
>
> Elena and Matteo
>
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