From ab5448fdcee3ed90b49cc102c1963600960bfa23 Mon Sep 17 00:00:00 2001
From: Timo Heister <timo.heister@gmail.com>
Date: Tue, 14 Oct 2014 16:19:34 -0400
Subject: [PATCH] Allow v=0.0 for ghosted PETSc and Trilinos vectors

---
 doc/news/changes.h                         |  6 ++++++
 include/deal.II/lac/trilinos_vector_base.h |  4 ----
 source/lac/petsc_vector_base.cc            | 16 ++++++++++++++--
 3 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/doc/news/changes.h b/doc/news/changes.h
index 0665d082ae..ce74a29e2b 100644
--- a/doc/news/changes.h
+++ b/doc/news/changes.h
@@ -307,6 +307,12 @@ inconvenience this causes.
 <h3>Specific improvements</h3>
 
 <ol>
+  <li> Changed: PETSc and Trilinos vectors with ghost entries can now be reset to zero
+  using = 0.0;
+  <br>
+  (Timo Heister, 2014/10/14)
+  </li>
+
   <li> New: The new function FiniteElement::get_associated_geometry_primitive() allows to
   query whether a given degree of freedom is associated with a vertex, line,
   quad, or hex.
diff --git a/include/deal.II/lac/trilinos_vector_base.h b/include/deal.II/lac/trilinos_vector_base.h
index dd8fc22fc9..449c4a5cf0 100644
--- a/include/deal.II/lac/trilinos_vector_base.h
+++ b/include/deal.II/lac/trilinos_vector_base.h
@@ -1227,10 +1227,6 @@ namespace TrilinosWrappers
   VectorBase &
   VectorBase::operator = (const TrilinosScalar s)
   {
-    // if we have ghost values, do not allow
-    // writing to this vector at all.
-    Assert (!has_ghost_elements(), ExcGhostsPresent());
-
     Assert (numbers::is_finite(s), ExcNumberNotFinite());
 
     const int ierr = vector->PutScalar(s);
diff --git a/source/lac/petsc_vector_base.cc b/source/lac/petsc_vector_base.cc
index 4bb7c835ed..007453082d 100644
--- a/source/lac/petsc_vector_base.cc
+++ b/source/lac/petsc_vector_base.cc
@@ -213,14 +213,26 @@ namespace PETScWrappers
   VectorBase &
   VectorBase::operator = (const PetscScalar s)
   {
-    Assert (!has_ghost_elements(), ExcGhostsPresent());
     Assert (numbers::is_finite(s), ExcNumberNotFinite());
 
     //TODO[TH]: assert(is_compressed())
 
-    const int ierr = VecSet (vector, s);
+    int ierr = VecSet (vector, s);
     AssertThrow (ierr == 0, ExcPETScError(ierr));
 
+    if (has_ghost_elements())
+    {
+      Vec ghost = PETSC_NULL;
+      ierr = VecGhostGetLocalForm(vector, &ghost);
+      AssertThrow (ierr == 0, ExcPETScError(ierr));
+
+      ierr = VecSet (ghost, s);
+      AssertThrow (ierr == 0, ExcPETScError(ierr));
+
+      ierr = VecGhostRestoreLocalForm(vector, &ghost);
+      AssertThrow (ierr == 0, ExcPETScError(ierr));
+    }
+    
     return *this;
   }
 
-- 
2.39.5