add missed files
diff --git a/src/main/java/org/apache/horn/funcs/FunctionFactory.java b/src/main/java/org/apache/horn/funcs/FunctionFactory.java
new file mode 100644
index 0000000..9b38a0d
--- /dev/null
+++ b/src/main/java/org/apache/horn/funcs/FunctionFactory.java
@@ -0,0 +1,68 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you 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.apache.horn.funcs;
+
+import org.apache.hama.commons.math.DoubleDoubleFunction;
+import org.apache.hama.commons.math.DoubleFunction;
+
+/**
+ * Factory to create the functions.
+ *
+ */
+public class FunctionFactory {
+
+ /**
+ * Create a double function with specified name.
+ *
+ * @param functionName
+ * @return an appropriate double function.
+ */
+ public static DoubleFunction createDoubleFunction(String functionName) {
+ if (functionName.equalsIgnoreCase(Sigmoid.class.getSimpleName())) {
+ return new Sigmoid();
+ } else if (functionName.equalsIgnoreCase(Tanh.class.getSimpleName())) {
+ return new Tanh();
+ } else if (functionName.equalsIgnoreCase(IdentityFunction.class
+ .getSimpleName())) {
+ return new IdentityFunction();
+ }
+
+ throw new IllegalArgumentException(String.format(
+ "No double function with name '%s' exists.", functionName));
+ }
+
+ /**
+ * Create a double double function with specified name.
+ *
+ * @param functionName
+ * @return an appropriate double double function.
+ */
+ public static DoubleDoubleFunction createDoubleDoubleFunction(
+ String functionName) {
+ if (functionName.equalsIgnoreCase(SquaredError.class.getSimpleName())) {
+ return new SquaredError();
+ } else if (functionName
+ .equalsIgnoreCase(CrossEntropy.class.getSimpleName())) {
+ return new CrossEntropy();
+ }
+
+ throw new IllegalArgumentException(String.format(
+ "No double double function with name '%s' exists.", functionName));
+ }
+
+}
\ No newline at end of file
diff --git a/src/main/java/org/apache/horn/funcs/IdentityFunction.java b/src/main/java/org/apache/horn/funcs/IdentityFunction.java
new file mode 100644
index 0000000..01e2e67
--- /dev/null
+++ b/src/main/java/org/apache/horn/funcs/IdentityFunction.java
@@ -0,0 +1,38 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you 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.apache.horn.funcs;
+
+import org.apache.hama.commons.math.DoubleFunction;
+
+/**
+ * The identity function f(x) = x.
+ *
+ */
+public class IdentityFunction extends DoubleFunction {
+
+ @Override
+ public double apply(double value) {
+ return value;
+ }
+
+ @Override
+ public double applyDerivative(double value) {
+ return 1;
+ }
+
+}
\ No newline at end of file
