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

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
+    const label nTotalCoarseCells = returnReduce(nCoarseCells, sumOp<label>());
-    bool contAgg = nCoarseCells >= nCellsInCoarsestLevel_;
+    if (nTotalCoarseCells >= Pstream::nProcs()*nCellsInCoarsestLevel_)
-    mesh().reduce(contAgg, andOp<bool>());
+    {
-    return contAgg;
+        return true;
+    }
+    else
+    {
+        const label nTotalFineCells = returnReduce(nFineCells, sumOp<label>());
+        return nTotalCoarseCells < nTotalFineCells;
+    }
 }
 
 

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>

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);