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.solvers; 018 019 import org.apache.commons.math3.util.FastMath; 020 import org.apache.commons.math3.exception.TooManyEvaluationsException; 021 022 /** 023 * Implements the <a href="http://mathworld.wolfram.com/Bisection.html"> 024 * bisection algorithm</a> for finding zeros of univariate real functions. 025 * <p> 026 * The function should be continuous but not necessarily smooth.</p> 027 * 028 * @version $Id: BisectionSolver.java 1391927 2012-09-30 00:03:30Z erans $ 029 */ 030 public class BisectionSolver extends AbstractUnivariateSolver { 031 /** Default absolute accuracy. */ 032 private static final double DEFAULT_ABSOLUTE_ACCURACY = 1e-6; 033 034 /** 035 * Construct a solver with default accuracy (1e-6). 036 */ 037 public BisectionSolver() { 038 this(DEFAULT_ABSOLUTE_ACCURACY); 039 } 040 /** 041 * Construct a solver. 042 * 043 * @param absoluteAccuracy Absolute accuracy. 044 */ 045 public BisectionSolver(double absoluteAccuracy) { 046 super(absoluteAccuracy); 047 } 048 /** 049 * Construct a solver. 050 * 051 * @param relativeAccuracy Relative accuracy. 052 * @param absoluteAccuracy Absolute accuracy. 053 */ 054 public BisectionSolver(double relativeAccuracy, 055 double absoluteAccuracy) { 056 super(relativeAccuracy, absoluteAccuracy); 057 } 058 059 /** 060 * {@inheritDoc} 061 */ 062 @Override 063 protected double doSolve() 064 throws TooManyEvaluationsException { 065 double min = getMin(); 066 double max = getMax(); 067 verifyInterval(min, max); 068 final double absoluteAccuracy = getAbsoluteAccuracy(); 069 double m; 070 double fm; 071 double fmin; 072 073 while (true) { 074 m = UnivariateSolverUtils.midpoint(min, max); 075 fmin = computeObjectiveValue(min); 076 fm = computeObjectiveValue(m); 077 078 if (fm * fmin > 0) { 079 // max and m bracket the root. 080 min = m; 081 } else { 082 // min and m bracket the root. 083 max = m; 084 } 085 086 if (FastMath.abs(max - min) <= absoluteAccuracy) { 087 m = UnivariateSolverUtils.midpoint(min, max); 088 return m; 089 } 090 } 091 } 092 }