[petsc-users] Preconditioner for LSC

[Elena Travaglia]

Thank you for the replay.

Now I have set the precondition on the command line with
"-fieldsplit_1_lsc_pc_type" , but is it also possible to set it from within
the code instead?
What is the equivalent code to obtain the effect of
"-fieldsplit_1_lsc_pc_type mat" ?

Elena

Il giorno mer 24 feb 2021 alle ore 06:04 Jed Brown <jed at jedbrown.org> ha
scritto:

> 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
> >
> > --
> > ------------------------
> >
> >
> >
> > Indirizzo istituzionale di posta elettronica
> > degli studenti e dei laureati dell'Università degli Studi di
> TorinoOfficial
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>

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degli studenti e dei laureati dell'Università degli Studi di TorinoOfficial 
University of Turin email address for students and graduates 
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