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

[Lawrence Mitchell]

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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:

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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