From 1edbaf94f2d32e933ae1900076ac89ff8ac9e884 Mon Sep 17 00:00:00 2001
From: msteigemann <msteigemann@yahoo.de>
Date: Thu, 21 May 2015 07:53:24 +0200
Subject: [PATCH] Add a clear function for PETSc serial and parallel vectors

---
 doc/news/changes.h                          |  6 ++++++
 include/deal.II/lac/petsc_parallel_vector.h |  6 ++++++
 include/deal.II/lac/petsc_vector.h          |  6 ++++++
 include/deal.II/lac/petsc_vector_base.h     |  6 ++++++
 source/lac/petsc_parallel_vector.cc         | 18 ++++++++++++++++++
 source/lac/petsc_vector.cc                  |  9 +++++++++
 source/lac/petsc_vector_base.cc             | 21 +++++++++++++++++++++
 7 files changed, 72 insertions(+)

diff --git a/doc/news/changes.h b/doc/news/changes.h
index 1d9097ce29..82eb390009 100644
--- a/doc/news/changes.h
+++ b/doc/news/changes.h
@@ -512,6 +512,12 @@ inconvenience this causes.
 <h3>Specific improvements</h3>
 
 <ol>
+  <li> New: Add a clear function to the PETSc::Vector
+  and PETSc::MPI::Vector classes similar to the Trilinos vector classes.
+  <br>
+  (Martin Steigemann 2015/05/22)
+  </li>
+
   <li> New: Three new quadrature formulas in quadrature_lib, based on
   Chebyshev quadrature rules. See functions QGaussChebyshev,
   QGaussRadauChebyshev and QGaussLobattoChebyshev.
diff --git a/include/deal.II/lac/petsc_parallel_vector.h b/include/deal.II/lac/petsc_parallel_vector.h
index 1b987c3417..ca7a3449db 100644
--- a/include/deal.II/lac/petsc_parallel_vector.h
+++ b/include/deal.II/lac/petsc_parallel_vector.h
@@ -262,6 +262,12 @@ namespace PETScWrappers
       explicit Vector (const IndexSet &local,
                        const MPI_Comm &communicator);
 
+      /**
+       * Release all memory and return to a state just like after having called
+       * the default constructor.
+       */
+      void clear ();
+
       /**
        * Copy the given vector. Resize the present vector if necessary. Also
        * take over the MPI communicator of @p v.
diff --git a/include/deal.II/lac/petsc_vector.h b/include/deal.II/lac/petsc_vector.h
index c923ffc22e..5c907f0f83 100644
--- a/include/deal.II/lac/petsc_vector.h
+++ b/include/deal.II/lac/petsc_vector.h
@@ -118,6 +118,12 @@ namespace PETScWrappers
      */
     explicit Vector (const MPI::Vector &v);
 
+    /**
+     * Release all memory and return to a state just like after having called
+     * the default constructor.
+     */
+    void clear ();
+
     /**
      * Copy the given vector. Resize the present vector if necessary.
      */
diff --git a/include/deal.II/lac/petsc_vector_base.h b/include/deal.II/lac/petsc_vector_base.h
index 4d60dfb11a..e17617ef06 100644
--- a/include/deal.II/lac/petsc_vector_base.h
+++ b/include/deal.II/lac/petsc_vector_base.h
@@ -260,6 +260,12 @@ namespace PETScWrappers
      */
     virtual ~VectorBase ();
 
+    /**
+     * Release all memory and return to a state just like after having called
+     * the default constructor.
+     */
+    virtual void clear ();
+
     /**
      * Compress the underlying representation of the PETSc object, i.e. flush
      * the buffers of the vector object if it has any. This function is
diff --git a/source/lac/petsc_parallel_vector.cc b/source/lac/petsc_parallel_vector.cc
index 87fde1ad6e..5037b9fc64 100644
--- a/source/lac/petsc_parallel_vector.cc
+++ b/source/lac/petsc_parallel_vector.cc
@@ -80,6 +80,7 @@ namespace PETScWrappers
     }
 
 
+
     Vector::Vector (const IndexSet   &local,
                     const MPI_Comm     &communicator)
       :
@@ -90,6 +91,23 @@ namespace PETScWrappers
     }
 
 
+
+    void
+    Vector::clear ()
+    {
+      // destroy the PETSc Vec and create an invalid empty vector,
+      // so we can just as well create a sequential one to avoid
+      // all the overhead incurred by parallelism
+      attained_ownership = true;
+      VectorBase::clear ();
+
+      const int n = 0;
+      int ierr = VecCreateSeq (PETSC_COMM_SELF, n, &vector);
+      AssertThrow (ierr == 0, ExcPETScError(ierr));
+    }
+
+
+
     void
     Vector::reinit (const MPI_Comm  &comm,
                     const size_type  n,
diff --git a/source/lac/petsc_vector.cc b/source/lac/petsc_vector.cc
index 0cf745a7b2..8baa0aeecf 100644
--- a/source/lac/petsc_vector.cc
+++ b/source/lac/petsc_vector.cc
@@ -61,6 +61,15 @@ namespace PETScWrappers
 
 
 
+  void
+  Vector::clear ()
+  {
+    VectorBase::clear ();
+    Vector::create_vector (0);
+  }
+
+
+
   void
   Vector::reinit (const size_type n,
                   const bool      fast)
diff --git a/source/lac/petsc_vector_base.cc b/source/lac/petsc_vector_base.cc
index b127024d25..0feeaef91a 100644
--- a/source/lac/petsc_vector_base.cc
+++ b/source/lac/petsc_vector_base.cc
@@ -210,6 +210,27 @@ namespace PETScWrappers
 
 
 
+  void
+  VectorBase::clear ()
+  {
+    if (attained_ownership)
+      {
+#if DEAL_II_PETSC_VERSION_LT(3,2,0)
+        const int ierr = VecDestroy (vector);
+#else
+        const int ierr = VecDestroy (&vector);
+#endif
+        AssertThrow (ierr == 0, ExcPETScError(ierr));
+      }
+
+    ghosted = false;
+    ghost_indices.clear ();
+    last_action = ::dealii::VectorOperation::unknown;
+    attained_ownership = true;
+  }
+
+
+
   VectorBase &
   VectorBase::operator = (const PetscScalar s)
   {
-- 
2.39.5