From eb95c3b93f6f45ced5fd9ada03db5d154c4f1156 Mon Sep 17 00:00:00 2001
From: heister <heister@0785d39b-7218-0410-832d-ea1e28bc413d>
Date: Sat, 2 Nov 2013 11:26:56 +0000
Subject: [PATCH] allow parallel::distributed::Triangulation::load/save with
 different number of CPUs

git-svn-id: https://svn.dealii.org/trunk@31508 0785d39b-7218-0410-832d-ea1e28bc413d
---
 deal.II/doc/news/changes.h                 |  9 ++++++++-
 deal.II/include/deal.II/distributed/tria.h |  4 ++--
 deal.II/source/distributed/tria.cc         | 17 +++++++++++++++--
 3 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/deal.II/doc/news/changes.h b/deal.II/doc/news/changes.h
index 6960664c7e..b4eab15de5 100644
--- a/deal.II/doc/news/changes.h
+++ b/deal.II/doc/news/changes.h
@@ -94,10 +94,17 @@ inconvenience this causes.
 
 
 <ol>
+  <li> Changed: It is now possible to restore a parallel Triangulation
+  (and solutions) with a different number of processors it was saved with
+  using Triangulation::save() and Triangulation::load().
+  <br>
+  (Timo Heister, 2013/11/02)
+  </li>
+
   <li> Added support for Windows: It is now possible again to use gcc on Windows
   in order to compile the library. We support gcc-4.8.1 on Cygwin64 and MinGW-w64.
   <br>
-  (Matthias Maier, 2013/11/1)
+  (Matthias Maier, 2013/11/01)
   </li>
 
   <li> Changed: step-9, step-13 and step-14 have been converted to use the
diff --git a/deal.II/include/deal.II/distributed/tria.h b/deal.II/include/deal.II/distributed/tria.h
index 7375a4bd29..5cac19d2de 100644
--- a/deal.II/include/deal.II/distributed/tria.h
+++ b/deal.II/include/deal.II/distributed/tria.h
@@ -622,8 +622,8 @@ namespace parallel
 
       /**
        * Load the refinement information saved with save() back in. The mesh
-       * must contain the same coarse mesh that was used in save(). You need
-       * to load with the same number of CPUs that you saved with.
+       * must contain the same coarse mesh that was used in save(). You no
+       * longer need to load with the same number of CPUs that you saved with.
        */
       void load(const char *filename);
 
diff --git a/deal.II/source/distributed/tria.cc b/deal.II/source/distributed/tria.cc
index fae79cacfa..f61226ea89 100644
--- a/deal.II/source/distributed/tria.cc
+++ b/deal.II/source/distributed/tria.cc
@@ -2096,8 +2096,6 @@ namespace parallel
         std::string fname=std::string(filename)+".info";
         std::ifstream f(fname.c_str());
         f >> numcpus >> attached_size >> attached_count;
-        if (numcpus != Utilities::MPI::n_mpi_processes (mpi_communicator))
-          throw ExcInternalError();
       }
 
       attached_data_size = 0;
@@ -2110,6 +2108,21 @@ namespace parallel
                           this,
                           &connectivity);
 
+      if (numcpus != Utilities::MPI::n_mpi_processes (mpi_communicator))
+        {
+          // We are changing the number of CPUs so we need to repartition.
+          // Note that p4est actually distributes the cells between the changed
+          // number of CPUs and so everything works without this call, but
+          // this command changes the distribution for some reason, so we
+          // will leave it in here.
+          dealii::internal::p4est::functions<dim>::
+                partition (parallel_forest,
+                           /* prepare coarsening */ 1,
+                           /* weight_callback */ NULL);
+
+
+        }
+
       try
         {
           copy_local_forest_to_triangulation ();
-- 
2.39.5