Added a convenience createConstant method for DerivativeStructure.

Thanks to Ajo Fod.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@1517789 13f79535-47bb-0310-9956-ffa450edef68

src/main/java/org/apache/commons/math3/analysis/differentiation/DerivativeStructure.java

@@ -232,6 +232,20 @@ public class DerivativeStructure implements RealFieldElement<DerivativeStructure
         return compiler.getOrder();
     }
 
+    /** Create a constant compatible with instance order and number of parameters.
+     * <p>
+     * This method is a convenience factory method, it simply calls
+     * {@code new DerivativeStructure(getFreeParameters(), getOrder(), c)}
+     * </p>
+     * @param c value of the constant
+     * @return a constant compatible with instance order and number of parameters
+     * @see #DerivativeStructure(int, int, double)
+     * @since 3.3
+     */
+    public DerivativeStructure createConstant(final double c) {
+        return new DerivativeStructure(getFreeParameters(), getOrder(), c);
+    }
+
     /** {@inheritDoc}
      * @since 3.2
      */

src/test/java/org/apache/commons/math3/analysis/differentiation/DerivativeStructureTest.java

@@ -89,6 +89,15 @@ public class DerivativeStructureTest extends ExtendedFieldElementAbstractTest<De
         }
     }
 
+    @Test
+    public void testCreateConstant() {
+        DerivativeStructure a = new DerivativeStructure(3, 2, 0, 1.3);
+        DerivativeStructure b = a.createConstant(2.5);
+        Assert.assertEquals(a.getFreeParameters(), b.getFreeParameters());
+        Assert.assertEquals(a.getOrder(), b.getOrder());
+        checkEquals(a.getField().getOne().multiply(2.5), b, 1.0e-15);
+    }
+
     @Test
     public void testPrimitiveAdd() {
         for (int maxOrder = 1; maxOrder < 5; ++maxOrder) {