From 2971503fed85add086cb163d24ee5d402d631aab Mon Sep 17 00:00:00 2001
From: Mmanu Chaturvedi <mmanu.chaturvedi@kitware.com>
Date: Tue, 23 May 2017 17:12:36 -0400
Subject: [PATCH] Specializing numeric_limits For AutoDiffScalar

---
 unsupported/Eigen/src/AutoDiff/AutoDiffScalar.h |  7 +++++++
 unsupported/test/autodiff_scalar.cpp            | 14 ++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/unsupported/Eigen/src/AutoDiff/AutoDiffScalar.h b/unsupported/Eigen/src/AutoDiff/AutoDiffScalar.h
index d2808860c..279fe5cd3 100755
--- a/unsupported/Eigen/src/AutoDiff/AutoDiffScalar.h
+++ b/unsupported/Eigen/src/AutoDiff/AutoDiffScalar.h
@@ -683,4 +683,11 @@ template<typename DerType> struct NumTraits<AutoDiffScalar<DerType> >
 
 }
 
+namespace std {
+template <typename T>
+class numeric_limits<Eigen::AutoDiffScalar<T> >
+  : public numeric_limits<typename T::Scalar> {};
+
+}  // namespace std
+
 #endif // EIGEN_AUTODIFF_SCALAR_H
diff --git a/unsupported/test/autodiff_scalar.cpp b/unsupported/test/autodiff_scalar.cpp
index 4df2f5c57..3a78d6b8d 100644
--- a/unsupported/test/autodiff_scalar.cpp
+++ b/unsupported/test/autodiff_scalar.cpp
@@ -72,6 +72,19 @@ template<typename Scalar> void check_hyperbolic_functions()
   VERIFY_IS_APPROX(res3.derivatives().x(), Scalar(0.339540557256150));
 }
 
+template <typename Scalar>
+void check_limits_specialization()
+{
+  typedef Eigen::Matrix<Scalar, 1, 1> Deriv;
+  typedef Eigen::AutoDiffScalar<Deriv> AD;
+
+  typedef std::numeric_limits<AD> A;
+  typedef std::numeric_limits<Scalar> B;
+
+  bool res = std::is_base_of<B, A>::value;
+  VERIFY_IS_EQUAL(res, true);
+}
+
 void test_autodiff_scalar()
 {
   for(int i = 0; i < g_repeat; i++) {
@@ -79,5 +92,6 @@ void test_autodiff_scalar()
     CALL_SUBTEST_2( check_atan2<double>() );
     CALL_SUBTEST_3( check_hyperbolic_functions<float>() );
     CALL_SUBTEST_4( check_hyperbolic_functions<double>() );
+    CALL_SUBTEST_5( check_limits_specialization<double>());
   }
 }