From 5ad239d7ec1d43e0c670b5a36ab694df6d62058b Mon Sep 17 00:00:00 2001
From: Hrvoje Jasak <h.jasak@wikki.co.uk>
Date: Tue, 24 Jan 2017 16:44:43 +0000
Subject: [PATCH] Bugfix: simple matrix operations

---
 .../matrices/lduMatrix/lduMatrix/lduMatrix.H  | 31 ++++++++++---------
 .../lduMatrix/lduMatrix/lduMatrixOperations.C | 12 +++++++
 2 files changed, 28 insertions(+), 15 deletions(-)

diff --git a/src/foam/matrices/lduMatrix/lduMatrix/lduMatrix.H b/src/foam/matrices/lduMatrix/lduMatrix/lduMatrix.H
index d50fc6bf4..09c9805c7 100644
--- a/src/foam/matrices/lduMatrix/lduMatrix/lduMatrix.H
+++ b/src/foam/matrices/lduMatrix/lduMatrix/lduMatrix.H
@@ -258,10 +258,9 @@ public:
             );
 
 
-        // Destructor
-
-            virtual ~solver()
-            {}
+        //- Destructor
+        virtual ~solver()
+        {}
 
 
         // Member functions
@@ -418,10 +417,9 @@ public:
             );
 
 
-        // Destructor
-
-            virtual ~smoother()
-            {}
+        //- Destructor
+        virtual ~smoother()
+        {}
 
 
         // Member functions
@@ -556,10 +554,9 @@ public:
             );
 
 
-        // Destructor
-
-            virtual ~preconditioner()
-            {}
+        //- Destructor
+        virtual ~preconditioner()
+        {}
 
 
         // Member functions
@@ -635,9 +632,8 @@ public:
         }
 
 
-    // Destructor
-
-        virtual ~lduMatrix();
+    //- Destructor
+    virtual ~lduMatrix();
 
 
     // Member functions
@@ -700,6 +696,11 @@ public:
                 return (lowerPtr_);
             }
 
+            bool empty() const
+            {
+                return (!diagPtr_ && !lowerPtr_ && !upperPtr_);
+            }
+
             bool diagonal() const
             {
                 return (diagPtr_ && !lowerPtr_ && !upperPtr_);
diff --git a/src/foam/matrices/lduMatrix/lduMatrix/lduMatrixOperations.C b/src/foam/matrices/lduMatrix/lduMatrix/lduMatrixOperations.C
index a523b6198..6497d8374 100644
--- a/src/foam/matrices/lduMatrix/lduMatrix/lduMatrixOperations.C
+++ b/src/foam/matrices/lduMatrix/lduMatrix/lduMatrixOperations.C
@@ -143,6 +143,12 @@ void Foam::lduMatrix::negate()
 
 void Foam::lduMatrix::operator+=(const lduMatrix& A)
 {
+    // Escape empty matrix
+    if (A.empty())
+    {
+        return;
+    }
+    
     if (A.diagPtr_)
     {
         diag() += A.diag();
@@ -211,6 +217,12 @@ void Foam::lduMatrix::operator+=(const lduMatrix& A)
 
 void Foam::lduMatrix::operator-=(const lduMatrix& A)
 {
+    // Escape empty matrix
+    if (A.empty())
+    {
+        return;
+    }
+    
     if (A.diagPtr_)
     {
         diag() -= A.diag();