Added log function.

JIRA: MATH-158



git-svn-id: https://svn.apache.org/repos/asf/jakarta/commons/proper/math/trunk@549299 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/commons/math/util/MathUtils.java

@@ -118,6 +118,25 @@ public final class MathUtils {
         return result;
     }
     
+    /** 
+     * <p>Returns the 
+     * <a href="http://mathworld.wolfram.com/Logarithm.html">logarithm</a>
+     * for base <code>b</code> of <code>x</code>.
+     * </p>
+     * <p>Returns <code>NaN<code> if either argument is negative.  If 
+     * <code>base</code> is 0 and <code>x</code> is positive, 0 is returned.
+     * If <code>base</code> is positive and <code>x</code> is 0, 
+     * <code>Double.NEGATIVE_INFINITY</code> is returned.  If both arguments
+     * are 0, the result is <code>NaN</code>.</p>
+     * 
+     * @param base the base of the logarithm, must be greater than 0
+     * @param x argument, must be greater than 0
+     * @return the value of the logarithm - the number y such that base^y = x.
+     */ 
+    public static double log(double base, double x) {
+    	return Math.log(x)/Math.log(base);
+    }
+    
     /**
      * Returns a <code>double</code> representation of the <a
      * href="http://mathworld.wolfram.com/BinomialCoefficient.html"> Binomial

src/test/org/apache/commons/math/util/MathUtilsTest.java

@@ -444,6 +444,16 @@ public final class MathUtilsTest extends TestCase {
         } 
     }
     
+    public void testLog() {
+    	assertEquals(2.0, MathUtils.log(2,4), 0);
+    	assertEquals(3.0, MathUtils.log(2,8), 0);
+        assertTrue(Double.isNaN(MathUtils.log(-1, 1)));
+        assertTrue(Double.isNaN(MathUtils.log(1, -1)));
+        assertTrue(Double.isNaN(MathUtils.log(0, 0)));
+        assertEquals(0, MathUtils.log(0, 10), 0);
+        assertEquals(Double.NEGATIVE_INFINITY, MathUtils.log(10, 0), 0);
+    }
+    
     public void testGcd() {
         int a = 30;
         int b = 50;

xdocs/changes.xml

@@ -81,6 +81,9 @@ Commons Math Release Notes</title>
       <action dev="psteitz" type="fix" issue="MATH-166" due-to="Lukas Theussl">
         Increased default precision of Gamma and Beta functions.
       </action>
+      <action dev="psteitz" type="update" issue="MATH-158" due-to "Hasan Diwan">
+        Added log function to MathUtils.
+      </action>
     </release>
     <release version="1.1" date="2005-12-17"  
  description="This is a maintenance release containing bug fixes and enhancements.