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Java > Open Source Codes > org > apache > commons > math > analysis > BisectionSolver


1 /*
2  * Copyright 2003-2004 The Apache Software Foundation.
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  * http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 package org.apache.commons.math.analysis;
17
18 import org.apache.commons.math.FunctionEvaluationException;
19 import org.apache.commons.math.ConvergenceException;
20
21 /**
22  * Implements the <a HREF="http://mathworld.wolfram.com/Bisection.html">
23  * bisection algorithm</a> for finding zeros of univariate real functions.
24  * <p>
25  * The function should be continuous but not necessarily smooth.
26  *
27  * @version $Revision$ $Date: 2005-02-26 05:11:52 -0800 (Sat, 26 Feb 2005) $
28  */
29 public class BisectionSolver extends UnivariateRealSolverImpl {
30     
31     /** Serializable version identifier */
32     static final long serialVersionUID = 7137520585963699578L;
33     
34     /**
35      * Construct a solver for the given function.
36      *
37      * @param f function to solve.
38      */
39     public BisectionSolver(UnivariateRealFunction f) {
40         super(f, 100, 1E-6);
41     }
42
43     /**
44      * Find a zero in the given interval.
45      *
46      * @param min the lower bound for the interval.
47      * @param max the upper bound for the interval.
48      * @param initial the start value to use (ignored).
49      * @return the value where the function is zero
50      * @throws ConvergenceException the maximum iteration count is exceeded
51      * @throws FunctionEvaluationException if an error occurs evaluating
52      * the function
53      * @throws IllegalArgumentException if min is not less than max
54      */
55     public double solve(double min, double max, double initial)
56         throws ConvergenceException, FunctionEvaluationException {
57           
58         return solve(min, max);
59     }
60     
61     /**
62      * Find a zero root in the given interval.
63      *
64      * @param min the lower bound for the interval
65      * @param max the upper bound for the interval
66      * @return the value where the function is zero
67      * @throws ConvergenceException if the maximum iteration count is exceeded.
68      * @throws FunctionEvaluationException if an error occurs evaluating the
69      * function
70      * @throws IllegalArgumentException if min is not less than max
71      */
72     public double solve(double min, double max) throws ConvergenceException,
73         FunctionEvaluationException {
74         
75         clearResult();
76         verifyInterval(min,max);
77         double m;
78         double fm;
79         double fmin;
80         
81         int i = 0;
82         while (i < maximalIterationCount) {
83             m = UnivariateRealSolverUtils.midpoint(min, max);
84            fmin = f.value(min);
85            fm = f.value(m);
86
87             if (fm * fmin > 0.0) {
88                 // max and m bracket the root.
89 min = m;
90                 fmin = fm;
91             } else {
92                 // min and m bracket the root.
93 max = m;
94             }
95
96             if (Math.abs(max - min) <= absoluteAccuracy) {
97                 m = UnivariateRealSolverUtils.midpoint(min, max);
98                 setResult(m, i);
99                 return m;
100             }
101             ++i;
102         }
103         
104         throw new ConvergenceException
105             ("Maximum number of iterations exceeded: " + maximalIterationCount);
106     }
107 }
108
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