From faa6d0e4dad9530a05fc4015d3af213950e7df52 Mon Sep 17 00:00:00 2001
From: Henry Weller <http://cfd.direct>
Date: Tue, 6 Sep 2016 13:29:05 +0100
Subject: [PATCH] GAMGAgglomeration: Add support for nCellsInCoarsestLevel = 1
 and better agglomeration termination Patch provided by Mattijs Janssens
 Resolves bug-report http://bugs.openfoam.org/view.php?id=2226

---
 .../GAMGAgglomeration/GAMGAgglomeration.C         | 15 +++++++++++----
 .../GAMGAgglomeration/GAMGAgglomeration.H         |  6 +++++-
 .../pairGAMGAgglomeration/pairGAMGAgglomerate.C   |  2 +-
 3 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/src/OpenFOAM/matrices/lduMatrix/solvers/GAMG/GAMGAgglomerations/GAMGAgglomeration/GAMGAgglomeration.C b/src/OpenFOAM/matrices/lduMatrix/solvers/GAMG/GAMGAgglomerations/GAMGAgglomeration/GAMGAgglomeration.C
index 6f7665b944..eb73b6f436 100644
--- a/src/OpenFOAM/matrices/lduMatrix/solvers/GAMG/GAMGAgglomerations/GAMGAgglomeration/GAMGAgglomeration.C
+++ b/src/OpenFOAM/matrices/lduMatrix/solvers/GAMG/GAMGAgglomerations/GAMGAgglomeration/GAMGAgglomeration.C
@@ -206,13 +206,20 @@ void Foam::GAMGAgglomeration::compactLevels(const label nCreatedLevels)
 
 bool Foam::GAMGAgglomeration::continueAgglomerating
 (
+    const label nFineCells,
     const label nCoarseCells
 ) const
 {
-    // Check the need for further agglomeration on all processors
-    bool contAgg = nCoarseCells >= nCellsInCoarsestLevel_;
-    mesh().reduce(contAgg, andOp<bool>());
-    return contAgg;
+    const label nTotalCoarseCells = returnReduce(nCoarseCells, sumOp<label>());
+    if (nTotalCoarseCells >= Pstream::nProcs()*nCellsInCoarsestLevel_)
+    {
+        return true;
+    }
+    else
+    {
+        const label nTotalFineCells = returnReduce(nFineCells, sumOp<label>());
+        return nTotalCoarseCells < nTotalFineCells;
+    }
 }
 
 
diff --git a/src/OpenFOAM/matrices/lduMatrix/solvers/GAMG/GAMGAgglomerations/GAMGAgglomeration/GAMGAgglomeration.H b/src/OpenFOAM/matrices/lduMatrix/solvers/GAMG/GAMGAgglomerations/GAMGAgglomeration/GAMGAgglomeration.H
index fd94b55760..7019c67dae 100644
--- a/src/OpenFOAM/matrices/lduMatrix/solvers/GAMG/GAMGAgglomerations/GAMGAgglomeration/GAMGAgglomeration.H
+++ b/src/OpenFOAM/matrices/lduMatrix/solvers/GAMG/GAMGAgglomerations/GAMGAgglomeration/GAMGAgglomeration.H
@@ -152,7 +152,11 @@ protected:
         void compactLevels(const label nCreatedLevels);
 
         //- Check the need for further agglomeration
-        bool continueAgglomerating(const label nCoarseCells) const;
+        bool continueAgglomerating
+        (
+            const label nCells,
+            const label nCoarseCells
+        ) const;
 
         //- Gather value from all procIDs onto procIDs[0]
         template<class Type>
diff --git a/src/OpenFOAM/matrices/lduMatrix/solvers/GAMG/GAMGAgglomerations/pairGAMGAgglomeration/pairGAMGAgglomerate.C b/src/OpenFOAM/matrices/lduMatrix/solvers/GAMG/GAMGAgglomerations/pairGAMGAgglomeration/pairGAMGAgglomerate.C
index bf4c695bda..42133e69d0 100644
--- a/src/OpenFOAM/matrices/lduMatrix/solvers/GAMG/GAMGAgglomerations/pairGAMGAgglomeration/pairGAMGAgglomerate.C
+++ b/src/OpenFOAM/matrices/lduMatrix/solvers/GAMG/GAMGAgglomerations/pairGAMGAgglomeration/pairGAMGAgglomerate.C
@@ -54,7 +54,7 @@ void Foam::pairGAMGAgglomeration::agglomerate
             *faceWeightsPtr
         );
 
-        if (continueAgglomerating(nCoarseCells))
+        if (continueAgglomerating(finalAgglomPtr().size(), nCoarseCells))
         {
             nCells_[nCreatedLevels] = nCoarseCells;
             restrictAddressing_.set(nCreatedLevels, finalAgglomPtr);