From 0262897d75c086130006d3e3336091bf68d9c3d7 Mon Sep 17 00:00:00 2001
From: Angelos Mantzaflaris <filiatra@gmail.com>
Date: Mon, 7 Dec 2015 11:43:29 +0100
Subject: [PATCH] const correctness

---
 exprtk.hpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/exprtk.hpp b/exprtk.hpp
index a9aba4a..4ed4859 100644
--- a/exprtk.hpp
+++ b/exprtk.hpp
@@ -32069,7 +32069,7 @@ namespace exprtk
    }
 
    template <typename T>
-   inline T derivative(expression<T>& e,
+   inline T derivative(const expression<T>& e,
                        T& x,
                        const T& h = T(0.00000001))
    {
@@ -32088,7 +32088,7 @@ namespace exprtk
    }
 
    template <typename T>
-   inline T second_derivative(expression<T>& e,
+   inline T second_derivative(const expression<T>& e,
                               T& x,
                               const T& h = T(0.00001))
    {