From 7ea4631c84ca6240a99bbb092a3b86b98d057dea Mon Sep 17 00:00:00 2001
From: Hrvoje Jasak <h.jasak@wikki.co.uk>
Date: Fri, 22 Mar 2019 11:49:53 +0000
Subject: [PATCH] Stability fix: hinv inverse of truly singular tensors

---
 src/foam/primitives/Tensor/tensor/tensor.C | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/src/foam/primitives/Tensor/tensor/tensor.C b/src/foam/primitives/Tensor/tensor/tensor.C
index 3f14b5d23..942da8d16 100644
--- a/src/foam/primitives/Tensor/tensor/tensor.C
+++ b/src/foam/primitives/Tensor/tensor/tensor.C
@@ -658,6 +658,12 @@ tensor hinv(const tensor& t)
             zeroInv += tensor(sqr(eigVecs.y()));
         }
 
+        if (det(t + zeroInv) < VSMALL)
+        {
+            // Determinant is still zero.  Return zero inverse
+            return tensor::zero;
+        }
+
         return inv(t + zeroInv) - zeroInv;
     }
 }
@@ -705,6 +711,12 @@ symmTensor hinv(const symmTensor& t)
             zeroInv += sqr(eigVecs.y());
         }
 
+        if (det(t + zeroInv) < VSMALL)
+        {
+            // Determinant is still zero.  Return zero inverse
+            return symmTensor::zero;
+        }
+
         return inv(t + zeroInv) - zeroInv;
     }
 }