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 */
017package org.apache.commons.math3.analysis;
018
019/**
020 * An interface representing a univariate real function.
021 * <br/>
022 * When a <em>user-defined</em> function encounters an error during
023 * evaluation, the {@link #value(double) value} method should throw a
024 * <em>user-defined</em> unchecked exception.
025 * <br/>
026 * The following code excerpt shows the recommended way to do that using
027 * a root solver as an example, but the same construct is applicable to
028 * ODE integrators or optimizers.
029 *
030 * <pre>
031 * private static class LocalException extends RuntimeException {
032 *     // The x value that caused the problem.
033 *     private final double x;
034 *
035 *     public LocalException(double x) {
036 *         this.x = x;
037 *     }
038 *
039 *     public double getX() {
040 *         return x;
041 *     }
042 * }
043 *
044 * private static class MyFunction implements UnivariateFunction {
045 *     public double value(double x) {
046 *         double y = hugeFormula(x);
047 *         if (somethingBadHappens) {
048 *           throw new LocalException(x);
049 *         }
050 *         return y;
051 *     }
052 * }
053 *
054 * public void compute() {
055 *     try {
056 *         solver.solve(maxEval, new MyFunction(a, b, c), min, max);
057 *     } catch (LocalException le) {
058 *         // Retrieve the x value.
059 *     }
060 * }
061 * </pre>
062 *
063 * As shown, the exception is local to the user's code and it is guaranteed
064 * that Apache Commons Math will not catch it.
065 *
066 * @version $Id: UnivariateFunction.java 1364387 2012-07-22 18:14:11Z tn $
067 */
068public interface UnivariateFunction {
069    /**
070     * Compute the value of the function.
071     *
072     * @param x Point at which the function value should be computed.
073     * @return the value of the function.
074     * @throws IllegalArgumentException when the activated method itself can
075     * ascertain that a precondition, specified in the API expressed at the
076     * level of the activated method, has been violated.
077     * When Commons Math throws an {@code IllegalArgumentException}, it is
078     * usually the consequence of checking the actual parameters passed to
079     * the method.
080     */
081    double value(double x);
082}