From a739ab8ff7d706d1c1b263dd47d8c4ac2dafc490 Mon Sep 17 00:00:00 2001
From: "Curtis C. Ober" <ccober@sandia.gov>
Date: Fri, 22 Mar 2019 10:05:36 -0600
Subject: [PATCH] Tempus: Fix Divide by Zero

In the relative norm calculation, the denominator is not check if
it is zero during the consistency check.  Fix it.

All Tempus tests pass.

 #4698
---
 packages/tempus/src/Tempus_StepperImplicit_impl.hpp | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/packages/tempus/src/Tempus_StepperImplicit_impl.hpp b/packages/tempus/src/Tempus_StepperImplicit_impl.hpp
index e83bfd3b07b2..19f79f23fb61 100644
--- a/packages/tempus/src/Tempus_StepperImplicit_impl.hpp
+++ b/packages/tempus/src/Tempus_StepperImplicit_impl.hpp
@@ -212,7 +212,11 @@ void StepperImplicit<Scalar>::setInitialConditions(
 
     this->evaluateImplicitODE(f, x, xDot, time, p);
 
-    Scalar reldiff = Thyra::norm(*f)/Thyra::norm(*x);
+    Scalar normX = Thyra::norm(*x);
+    Scalar reldiff = Scalar(0.0);
+    if (normX == Scalar(0.0)) reldiff = Thyra::norm(*f);
+    else reldiff = Thyra::norm(*f)/normX;
+
     Scalar eps = Scalar(100.0)*std::abs(Teuchos::ScalarTraits<Scalar>::eps());
     if (reldiff > eps) {
       RCP<Teuchos::FancyOStream> out = this->getOStream();