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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.commons.math3.analysis;
18  
19  /**
20   * An interface representing a univariate real function.
21   * <br/>
22   * When a <em>user-defined</em> function encounters an error during
23   * evaluation, the {@link #value(double) value} method should throw a
24   * <em>user-defined</em> unchecked exception.
25   * <br/>
26   * The following code excerpt shows the recommended way to do that using
27   * a root solver as an example, but the same construct is applicable to
28   * ODE integrators or optimizers.
29   *
30   * <pre>
31   * private static class LocalException extends RuntimeException {
32   *     // The x value that caused the problem.
33   *     private final double x;
34   *
35   *     public LocalException(double x) {
36   *         this.x = x;
37   *     }
38   *
39   *     public double getX() {
40   *         return x;
41   *     }
42   * }
43   *
44   * private static class MyFunction implements UnivariateFunction {
45   *     public double value(double x) {
46   *         double y = hugeFormula(x);
47   *         if (somethingBadHappens) {
48   *           throw new LocalException(x);
49   *         }
50   *         return y;
51   *     }
52   * }
53   *
54   * public void compute() {
55   *     try {
56   *         solver.solve(maxEval, new MyFunction(a, b, c), min, max);
57   *     } catch (LocalException le) {
58   *         // Retrieve the x value.
59   *     }
60   * }
61   * </pre>
62   *
63   * As shown, the exception is local to the user's code and it is guaranteed
64   * that Apache Commons Math will not catch it.
65   *
66   * @version $Id: UnivariateFunction.java 1364387 2012-07-22 18:14:11Z tn $
67   */
68  public interface UnivariateFunction {
69      /**
70       * Compute the value of the function.
71       *
72       * @param x Point at which the function value should be computed.
73       * @return the value of the function.
74       * @throws IllegalArgumentException when the activated method itself can
75       * ascertain that a precondition, specified in the API expressed at the
76       * level of the activated method, has been violated.
77       * When Commons Math throws an {@code IllegalArgumentException}, it is
78       * usually the consequence of checking the actual parameters passed to
79       * the method.
80       */
81      double value(double x);
82  }