1 files changed, 90 insertions, 0 deletions
diff --git a/watchmaker/examples/src/java/main/org/uncommons/watchmaker/examples/geneticprogramming/Multiplication.java b/watchmaker/examples/src/java/main/org/uncommons/watchmaker/examples/geneticprogramming/Multiplication.java
new file mode 100644
index 0000000..bd5dd60
--- /dev/null
+++ b/watchmaker/examples/src/java/main/org/uncommons/watchmaker/examples/geneticprogramming/Multiplication.java
@@ -0,0 +1,90 @@
+//=============================================================================
+// Copyright 2006-2010 Daniel W. Dyer
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//=============================================================================
+package org.uncommons.watchmaker.examples.geneticprogramming;
+
+/**
+ * Simple multiplication operator {@link Node}.
+ * @author Daniel Dyer
+ */
+public class Multiplication extends BinaryNode
+{
+    /**
+     * Creates a node that evaluates to the product of the values of its two
+     * child nodes ({@literal left} and {@literal right}).
+     * @param left The first operand.
+     * @param right The second operand.
+     */
+    public Multiplication(Node left, Node right)
+    {
+        super(left, right, '*');
+    }
+
+
+    /**
+     * Evaluates the two sub-trees and returns the product of these two values.
+     * @param programParameters Program parameters (ignored by the multiplication operator
+     * but may be used in evaluating the sub-trees).
+     * @return The sum of the values of both child nodes.
+     */
+    public double evaluate(double[] programParameters)
+    {
+        return left.evaluate(programParameters) * right.evaluate(programParameters);
+    }
+
+
+    /**
+     * {@inheritDoc}
+     */
+    public Node simplify()
+    {
+        Node simplifiedLeft = left.simplify();
+        Node simplifiedRight = right.simplify();
+        // If the two arguments are constants, we can simplify by calculating the result, it won't
+        // ever change.
+        if (simplifiedLeft instanceof Constant && simplifiedRight instanceof Constant)
+        {
+            return new Constant(simplifiedLeft.evaluate(NO_ARGS) * simplifiedRight.evaluate(NO_ARGS));
+        }
+        // Multiplying by one is pointless, the expression can be reduced to its other argument.
+        else if (simplifiedRight instanceof Constant)
+        {
+            double constant = simplifiedRight.evaluate(NO_ARGS);
+            if (constant == 1)
+            {
+                return simplifiedLeft;
+            }
+            else if (constant == 0)
+            {
+                return new Constant(0);
+            }
+        }
+        else if (simplifiedLeft instanceof Constant)
+        {
+            double constant = simplifiedLeft.evaluate(NO_ARGS);
+            if (constant == 1)
+            {
+                return simplifiedRight;
+            }
+            else if (constant == 0)
+            {
+                return new Constant(0);
+            }
+        }
+        return simplifiedLeft != left || simplifiedRight != right
+               ? new Multiplication(simplifiedLeft, simplifiedRight)
+               : this;
+    }
+}