From 9227754177ba240cd51ad15517f3edc72a0641b3 Mon Sep 17 00:00:00 2001
From: Gilles Sadowski <erans@apache.org>
Date: Mon, 17 Oct 2011 14:05:53 +0000
Subject: [PATCH] Added "derivative".

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@1185184 13f79535-47bb-0310-9956-ffa450edef68
---
 .../commons/math/analysis/function/Log10.java    | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/src/main/java/org/apache/commons/math/analysis/function/Log10.java b/src/main/java/org/apache/commons/math/analysis/function/Log10.java
index f0464515b..a5af75996 100644
--- a/src/main/java/org/apache/commons/math/analysis/function/Log10.java
+++ b/src/main/java/org/apache/commons/math/analysis/function/Log10.java
@@ -18,6 +18,7 @@
 package org.apache.commons.math.analysis.function;
 
 import org.apache.commons.math.analysis.UnivariateRealFunction;
+import org.apache.commons.math.analysis.DifferentiableUnivariateRealFunction;
 import org.apache.commons.math.util.FastMath;
 
 /**
@@ -26,9 +27,22 @@ import org.apache.commons.math.util.FastMath;
  * @version $Id$
  * @since 3.0
  */
-public class Log10 implements UnivariateRealFunction {
+public class Log10 implements DifferentiableUnivariateRealFunction {
+    /** ln(10) = {@value}.*/
+    private static final double LN_10 = FastMath.log(10);
+
     /** {@inheritDoc} */
     public double value(double x) {
         return FastMath.log10(x);
     }
+
+    /** {@inheritDoc} */
+    public UnivariateRealFunction derivative() {
+        return new UnivariateRealFunction() {
+            /** {@inheritDoc} */
+            public double value(double x) {
+                return 1 / (x * LN_10);
+            }
+        };
+    }
 }