Added array-scaling methods to MathArrays. Patch provided by Jared Becksfort. JIRA: MATH-877

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@1457130 13f79535-47bb-0310-9956-ffa450edef68

src/changes/changes.xml

@@ -55,6 +55,9 @@ This is a minor release: It combines bug fixes and new features.
   Changes to existing features were made in a backwards-compatible
   way such as to allow drop-in replacement of the v3.1[.1] JAR file.
 ">
+      <action dev="psteitz" type="add" issue="MATH-946" due-to="Jared Becksfort">
+        Added array-scaling methods to MathArrays.
+      </action>
       <action dev="luc" type="update" issue="MATH-877" due-to="Peter Andrews">
         Allow direct use of SummaryStatistics in one-way ANOVA.
       </action>

src/main/java/org/apache/commons/math3/util/MathArrays.java

@@ -73,6 +73,35 @@ public class MathArrays {
                         int numElements);
     }
 
+    /**
+     * Create a copy of an array scaled by a value.
+     *
+     * @param arr Array to scale.
+     * @param val Scalar.
+     * @return scaled copy of array with each entry multiplied by val.
+     */
+    public static double[] scale(double val, final double[] arr) {
+        double[] newArr = new double[arr.length];
+        for (int i = 0; i < arr.length; i++) {
+            newArr[i] = arr[i] * val;
+        }
+        return newArr;
+    }
+
+    /**
+     * <p>Multiply each element of an array by a value.</p>
+     *
+     * <p>The array is modified in place (no copy is created).</p>
+     *
+     * @param arr Array to scale
+     * @param val Scalar
+     */
+    public static void scaleInPlace(double val, final double[] arr) {
+        for (int i = 0; i < arr.length; i++) {
+            arr[i] *= val;
+        }
+    }
+
     /**
      * Creates an array whose contents will be the element-by-element
      * addition of the arguments.

src/test/java/org/apache/commons/math3/util/MathArraysTest.java

@@ -33,6 +33,38 @@ import org.junit.Test;
  * @version $Id$
  */
 public class MathArraysTest {
+    
+    @Test
+    public void testScale() {
+        final double[] test = new double[] { -2.5, -1, 0, 1, 2.5 };
+        final double[] correctTest = MathArrays.copyOf(test);
+        final double[] correctScaled = new double[]{5.25, 2.1, 0, -2.1, -5.25};
+        
+        final double[] scaled = MathArrays.scale(-2.1, test);
+
+        // Make sure test has not changed
+        for (int i = 0; i < test.length; i++) {
+            Assert.assertEquals(correctTest[i], test[i], 0);
+        }
+
+        // Test scaled values
+        for (int i = 0; i < scaled.length; i++) {
+            Assert.assertEquals(correctScaled[i], scaled[i], 0);
+        }
+    }
+    
+    @Test
+    public void testScaleInPlace() {
+        final double[] test = new double[] { -2.5, -1, 0, 1, 2.5 };
+        final double[] correctScaled = new double[]{5.25, 2.1, 0, -2.1, -5.25};
+        MathArrays.scaleInPlace(-2.1, test);
+
+        // Make sure test has changed
+        for (int i = 0; i < test.length; i++) {
+            Assert.assertEquals(correctScaled[i], test[i], 0);
+        }
+    }
+    
     @Test(expected=DimensionMismatchException.class)
     public void testEbeAddPrecondition() {
         MathArrays.ebeAdd(new double[3], new double[4]);