From 0ff31766e0c803518caaa7ec1af3e82178a16187 Mon Sep 17 00:00:00 2001
From: marcfehling <marc.fehling@gmx.net>
Date: Thu, 5 Dec 2019 21:53:58 +0100
Subject: [PATCH] Adjusted thresholds for refine_and_coarsen_fixed_number() for
 both GridRefinement and parallel::distributed::GridRefinement.

---
 doc/news/changes/incompatibilities/20191205Fehling1 | 6 ++++++
 source/distributed/grid_refinement.cc               | 4 ++--
 source/grid/grid_refinement.cc                      | 4 ++--
 3 files changed, 10 insertions(+), 4 deletions(-)
 create mode 100644 doc/news/changes/incompatibilities/20191205Fehling1

diff --git a/doc/news/changes/incompatibilities/20191205Fehling1 b/doc/news/changes/incompatibilities/20191205Fehling1
new file mode 100644
index 0000000000..a1e13526a5
--- /dev/null
+++ b/doc/news/changes/incompatibilities/20191205Fehling1
@@ -0,0 +1,6 @@
+Changed: Adjusted threshold for fixed number adaptation: The last qualifying
+cells for refinement and coarsening now specify their respective threshold.
+This affects both GridRefinement::fixed_number_refinement() and
+parallel::distributed::GridRefinement::fixed_number_refinement().
+<br>
+(Marc Fehling, 12/05/2019)
diff --git a/source/distributed/grid_refinement.cc b/source/distributed/grid_refinement.cc
index 8a89ceb141..47e9d439d2 100644
--- a/source/distributed/grid_refinement.cc
+++ b/source/distributed/grid_refinement.cc
@@ -481,8 +481,8 @@ namespace parallel
           bottom_threshold = RefineAndCoarsenFixedNumber::compute_threshold(
             locally_owned_indicators,
             global_min_and_max,
-            static_cast<unsigned int>((1 - adjusted_fractions.second) *
-                                      tria.n_global_active_cells()),
+            static_cast<unsigned int>(std::ceil(
+              (1 - adjusted_fractions.second) * tria.n_global_active_cells())),
             mpi_communicator);
         else
           {
diff --git a/source/grid/grid_refinement.cc b/source/grid/grid_refinement.cc
index 0c6af2b6cc..d60f062b7d 100644
--- a/source/grid/grid_refinement.cc
+++ b/source/grid/grid_refinement.cc
@@ -231,10 +231,10 @@ GridRefinement::refine_and_coarsen_fixed_number(
           else
             {
               std::nth_element(tmp.begin(),
-                               tmp.begin() + refine_cells,
+                               tmp.begin() + refine_cells - 1,
                                tmp.end(),
                                std::greater<double>());
-              refine(tria, criteria, *(tmp.begin() + refine_cells));
+              refine(tria, criteria, *(tmp.begin() + refine_cells - 1));
             }
         }
 
-- 
2.39.5