[petsc-dev] State restriction of snes solutions without rscale

[Jed Brown]

Lawrence Mitchell <lawrence.mitchell at imperial.ac.uk> writes:

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> Hi all,
>
> I provide both the state restriction matrix (DMCreateInjection) along
> with residual transfer (DMCreateInterpolation), and therefore don't
> provide the (optional) scaling vector in DMCreateInterpolation.
> However, DMRestrictHook_SNESVecSol, called indirectly during
> SNESSolve_FAS just does:
>
>   ierr = MatRestrict(Restrict,Xfine,Xcoarse);CHKERRQ(ierr);
>   ierr = VecPointwiseMult(Xcoarse,Xcoarse,Rscale);CHKERRQ(ierr);
>
> Which fails if Rscale hasn't been provided.
>
> How about using the Inject matrix first if the user has provided it?
> Something like:

Yes, Inject should be preferred.

> diff --git a/src/snes/interface/snes.c b/src/snes/interface/snes.c
> index cc9cc30..d037650 100644
> - --- a/src/snes/interface/snes.c
> +++ b/src/snes/interface/snes.c
> @@ -481,8 +481,12 @@ static PetscErrorCode
> DMRestrictHook_SNESVecSol(DM dmfine,Mat Restrict,Vec Rscal
>      Xfine = Xfine_named;
>    }
>    ierr =
> DMGetNamedGlobalVector(dmcoarse,"SNESVecSol",&Xcoarse);CHKERRQ(ierr);
> - -  ierr = MatRestrict(Restrict,Xfine,Xcoarse);CHKERRQ(ierr);
> - -  ierr = VecPointwiseMult(Xcoarse,Xcoarse,Rscale);CHKERRQ(ierr);
> +  if (Inject) {
> +    ierr = MatRestrict(Inject,Xfine,Xcoarse);CHKERRQ(ierr);
> +  } else {
> +    ierr = MatRestrict(Restrict,Xfine,Xcoarse);CHKERRQ(ierr);
> +    ierr = VecPointwiseMult(Xcoarse,Xcoarse,Rscale);CHKERRQ(ierr);
> +  }
>    ierr =
> DMRestoreNamedGlobalVector(dmcoarse,"SNESVecSol",&Xcoarse);CHKERRQ(ierr);
>    if (Xfine_named) {ierr =
> DMRestoreNamedGlobalVector(dmfine,"SNESVecSol",&Xfine_named);CHKERRQ(ierr);}
>    PetscFunctionReturn(0);
>
> Cheers,
>
> Lawrence
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