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 package 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 */
068 public 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 }