001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017
018package org.apache.commons.math3.analysis.function;
019
020import org.apache.commons.math3.analysis.DifferentiableUnivariateFunction;
021import org.apache.commons.math3.analysis.differentiation.DerivativeStructure;
022import org.apache.commons.math3.analysis.differentiation.UnivariateDifferentiableFunction;
023
024/**
025 * Identity function.
026 *
027 * @since 3.0
028 */
029public class Identity implements UnivariateDifferentiableFunction, DifferentiableUnivariateFunction {
030    /** {@inheritDoc} */
031    public double value(double x) {
032        return x;
033    }
034
035    /** {@inheritDoc}
036     * @deprecated as of 3.1, replaced by {@link #value(DerivativeStructure)}
037     */
038    @Deprecated
039    public DifferentiableUnivariateFunction derivative() {
040        return new Constant(1);
041    }
042
043    /** {@inheritDoc}
044     * @since 3.1
045     */
046    public DerivativeStructure value(final DerivativeStructure t) {
047        return t;
048    }
049
050}