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
18 package org.apache.commons.math4.legacy.analysis.solvers;
19
20 /**
21 * Implements the <em>Pegasus</em> method for root-finding (approximating
22 * a zero of a univariate real function). It is a modified
23 * {@link RegulaFalsiSolver <em>Regula Falsi</em>} method.
24 *
25 * <p>Like the <em>Regula Falsi</em> method, convergence is guaranteed by
26 * maintaining a bracketed solution. The <em>Pegasus</em> method however,
27 * should converge much faster than the original <em>Regula Falsi</em>
28 * method. Furthermore, this implementation of the <em>Pegasus</em> method
29 * should not suffer from the same implementation issues as the <em>Regula
30 * Falsi</em> method, which may fail to convergence in certain cases. Also,
31 * the <em>Pegasus</em> method should converge faster than the
32 * {@link IllinoisSolver <em>Illinois</em>} method, another <em>Regula
33 * Falsi</em>-based method.</p>
34 *
35 * <p>The <em>Pegasus</em> method assumes that the function is continuous,
36 * but not necessarily smooth.</p>
37 *
38 * <p>Implementation based on the following article: M. Dowell and P. Jarratt,
39 * <em>The "Pegasus" method for computing the root of an equation</em>,
40 * BIT Numerical Mathematics, volume 12, number 4, pages 503-508, Springer,
41 * 1972.</p>
42 *
43 * @since 3.0
44 */
45 public class PegasusSolver extends BaseSecantSolver {
46
47 /** Construct a solver with default accuracy (1e-6). */
48 public PegasusSolver() {
49 super(DEFAULT_ABSOLUTE_ACCURACY, Method.PEGASUS);
50 }
51
52 /**
53 * Construct a solver.
54 *
55 * @param absoluteAccuracy Absolute accuracy.
56 */
57 public PegasusSolver(final double absoluteAccuracy) {
58 super(absoluteAccuracy, Method.PEGASUS);
59 }
60
61 /**
62 * Construct a solver.
63 *
64 * @param relativeAccuracy Relative accuracy.
65 * @param absoluteAccuracy Absolute accuracy.
66 */
67 public PegasusSolver(final double relativeAccuracy,
68 final double absoluteAccuracy) {
69 super(relativeAccuracy, absoluteAccuracy, Method.PEGASUS);
70 }
71
72 /**
73 * Construct a solver.
74 *
75 * @param relativeAccuracy Relative accuracy.
76 * @param absoluteAccuracy Absolute accuracy.
77 * @param functionValueAccuracy Maximum function value error.
78 */
79 public PegasusSolver(final double relativeAccuracy,
80 final double absoluteAccuracy,
81 final double functionValueAccuracy) {
82 super(relativeAccuracy, absoluteAccuracy, functionValueAccuracy, Method.PEGASUS);
83 }
84 }