From 09c81ac03335584674371369d0045510dc83aba4 Mon Sep 17 00:00:00 2001
From: Gael Guennebaud <g.gael@free.fr>
Date: Sat, 4 Aug 2018 00:17:37 +0200
Subject: [PATCH] bug #1451: fix numeric_limits<AutoDiffScalar<Der>> with a
 reference as derivative type

---
 unsupported/Eigen/src/AutoDiff/AutoDiffScalar.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/unsupported/Eigen/src/AutoDiff/AutoDiffScalar.h b/unsupported/Eigen/src/AutoDiff/AutoDiffScalar.h
index 279fe5cd3..13d959df4 100755
--- a/unsupported/Eigen/src/AutoDiff/AutoDiffScalar.h
+++ b/unsupported/Eigen/src/AutoDiff/AutoDiffScalar.h
@@ -684,10 +684,15 @@ template<typename DerType> struct NumTraits<AutoDiffScalar<DerType> >
 }
 
 namespace std {
+
 template <typename T>
 class numeric_limits<Eigen::AutoDiffScalar<T> >
   : public numeric_limits<typename T::Scalar> {};
 
+template <typename T>
+class numeric_limits<Eigen::AutoDiffScalar<T&> >
+  : public numeric_limits<typename T::Scalar> {};
+
 }  // namespace std
 
 #endif // EIGEN_AUTODIFF_SCALAR_H