Created "natural" method in "MathArrays" from code previously in

class "RandomDataGenerator" (private method).


git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@1520619 13f79535-47bb-0310-9956-ffa450edef68

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

@@ -1533,4 +1533,19 @@ public class MathArrays {
     public static void shuffle(int[] list) {
         shuffle(list, new Well19937c());
     }
+
+    /**
+     * Returns an array representing the natural number {@code n}.
+     *
+     * @param n Natural number.
+     * @return an array whose entries are the numbers 0, 1, ..., {@code n}-1.
+     * If {@code n == 0}, the returned array is empty.
+     */
+    public static int[] natural(int n) {
+        final int[] a = new int[n];
+        for (int i = 0; i < n; i++) {
+            a[i] = i;
+        }
+        return a;
+    }
 }

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

@@ -979,4 +979,21 @@ public class MathArraysTest {
         }
         Assert.assertTrue(ok);
     }
+
+    @Test
+    public void testNatural() {
+        final int n = 4;
+        final int[] expected = {0, 1, 2, 3};
+
+        final int[] natural = MathArrays.natural(n);
+        for (int i = 0; i < n; i++) {
+            Assert.assertEquals(expected[i], natural[i]);
+        }
+    }
+
+    @Test
+    public void testNaturalZero() {
+        final int[] natural = MathArrays.natural(0);
+        Assert.assertEquals(natural.length, 0);
+    }
 }