ENH: GaussSeidelSmoother: avoid memory allocation - use in-place negation

src/OpenFOAM/matrices/lduMatrix/smoothers/GaussSeidel/GaussSeidelSmoother.C

@@ -107,16 +107,29 @@ void Foam::GaussSeidelSmoother::smooth
     // To compensate for this, it is necessary to turn the
     // sign of the contribution.
 
-    FieldField<Field, scalar> mBouCoeffs(interfaceBouCoeffs_.size());
-
+    //FieldField<Field, scalar> mBouCoeffs(interfaceBouCoeffs_.size());
+    //
+    //forAll(mBouCoeffs, patchi)
+    //{
+    //    if (interfaces_.set(patchi))
+    //    {
+    //        mBouCoeffs.set(patchi, -interfaceBouCoeffs_[patchi]);
+    //    }
+    //}
+    FieldField<Field, scalar>& mBouCoeffs =
+        const_cast<FieldField<Field, scalar>&>
+        (
+            interfaceBouCoeffs_
+        );
     forAll(mBouCoeffs, patchi)
     {
         if (interfaces_.set(patchi))
         {
-            mBouCoeffs.set(patchi, -interfaceBouCoeffs_[patchi]);
+            mBouCoeffs[patchi].negate();
         }
     }
 
+
     for (label sweep=0; sweep<nSweeps; sweep++)
     {
         bPrime = source;
@@ -170,6 +183,15 @@ void Foam::GaussSeidelSmoother::smooth
             psiPtr[cellI] = curPsi;
         }
     }
+
+    // Restore interfaceBouCoeffs_
+    forAll(mBouCoeffs, patchi)
+    {
+        if (interfaces_.set(patchi))
+        {
+            mBouCoeffs[patchi].negate();
+        }
+    }
 }