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.math4.legacy.analysis;
18
19 import java.util.function.DoubleUnaryOperator;
20
21 /**
22 * An interface representing a univariate real function.
23 * <p>
24 * When a <em>user-defined</em> function encounters an error during
25 * evaluation, the {@link #value(double) value} method should throw a
26 * <em>user-defined</em> unchecked exception.</p>
27 * <p>
28 * The following code excerpt shows the recommended way to do that using
29 * a root solver as an example, but the same construct is applicable to
30 * ODE integrators or optimizers.</p>
31 *
32 * <pre>
33 * private static class LocalException extends RuntimeException {
34 * // The x value that caused the problem.
35 * private final double x;
36 *
37 * public LocalException(double x) {
38 * this.x = x;
39 * }
40 *
41 * public double getX() {
42 * return x;
43 * }
44 * }
45 *
46 * private static class MyFunction implements UnivariateFunction {
47 * public double value(double x) {
48 * double y = hugeFormula(x);
49 * if (somethingBadHappens) {
50 * throw new LocalException(x);
51 * }
52 * return y;
53 * }
54 * }
55 *
56 * public void compute() {
57 * try {
58 * solver.solve(maxEval, new MyFunction(a, b, c), min, max);
59 * } catch (LocalException le) {
60 * // Retrieve the x value.
61 * }
62 * }
63 * </pre>
64 *
65 * As shown, the exception is local to the user's code and it is guaranteed
66 * that Apache Commons Math will not catch it.
67 */
68 @FunctionalInterface
69 public interface UnivariateFunction extends DoubleUnaryOperator {
70 /**
71 * Compute the value of the function.
72 *
73 * @param x Point at which the function value should be computed.
74 * @return the value of the function.
75 * @throws IllegalArgumentException when the activated method itself can
76 * ascertain that a precondition, specified in the API expressed at the
77 * level of the activated method, has been violated.
78 * When Commons Math throws an {@code IllegalArgumentException}, it is
79 * usually the consequence of checking the actual parameters passed to
80 * the method.
81 */
82 double value(double x);
83
84 /** {@inheritDoc} */
85 @Override
86 default double applyAsDouble(double x) {
87 return value(x);
88 }
89 }