From fe46fbdf723d6d13952f955d780576a1a06a8792 Mon Sep 17 00:00:00 2001
From: David Wells <wellsd2@rpi.edu>
Date: Sat, 9 Jan 2016 14:18:17 -0500
Subject: [PATCH] Improve the refine_mesh function.

---
 cdr/solver/cdr.cc | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/cdr/solver/cdr.cc b/cdr/solver/cdr.cc
index 3c37619..0be13d4 100644
--- a/cdr/solver/cdr.cc
+++ b/cdr/solver/cdr.cc
@@ -231,15 +231,15 @@ void CDRProblem<dim>::time_iterate()
 template<int dim>
 void CDRProblem<dim>::refine_mesh()
 {
-  parallel::distributed::SolutionTransfer<dim, TrilinosWrappers::MPI::Vector>
-  solution_transfer(dof_handler);
-
   Vector<float> estimated_error_per_cell(triangulation.n_active_cells());
   KellyErrorEstimator<dim>::estimate
   (dof_handler, QGauss<dim - 1>(fe.degree + 1), typename FunctionMap<dim>::type(),
    locally_relevant_solution, estimated_error_per_cell);
 
-  // Poor man's version of refine and coarsen
+  // This solver uses a crude refinement strategy where cells with relatively
+  // high errors are refined and cells with relatively low errors are
+  // coarsened. The maximum refinement level is capped to prevent run-away
+  // refinement.
   for (const auto &cell : triangulation.active_cell_iterators())
     {
       if (std::abs(estimated_error_per_cell[cell->active_cell_index()]) >= 1e-3)
@@ -261,9 +261,14 @@ void CDRProblem<dim>::refine_mesh()
         }
     }
 
+  // Transferring the solution between different grids is ultimately just a
+  // few function calls but they must be made in exactly the right order.
+  parallel::distributed::SolutionTransfer<dim, TrilinosWrappers::MPI::Vector>
+    solution_transfer(dof_handler);
+
   triangulation.prepare_coarsening_and_refinement();
   solution_transfer.prepare_for_coarsening_and_refinement
-  (locally_relevant_solution);
+    (locally_relevant_solution);
   triangulation.execute_coarsening_and_refinement();
 
   setup_dofs();
-- 
2.39.5