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 */ 017package org.apache.commons.math3.analysis.solvers; 018 019import org.apache.commons.math3.util.FastMath; 020import 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 */ 029public class BisectionSolver extends AbstractUnivariateSolver { 030 /** Default absolute accuracy. */ 031 private static final double DEFAULT_ABSOLUTE_ACCURACY = 1e-6; 032 033 /** 034 * Construct a solver with default accuracy (1e-6). 035 */ 036 public BisectionSolver() { 037 this(DEFAULT_ABSOLUTE_ACCURACY); 038 } 039 /** 040 * Construct a solver. 041 * 042 * @param absoluteAccuracy Absolute accuracy. 043 */ 044 public BisectionSolver(double absoluteAccuracy) { 045 super(absoluteAccuracy); 046 } 047 /** 048 * Construct a solver. 049 * 050 * @param relativeAccuracy Relative accuracy. 051 * @param absoluteAccuracy Absolute accuracy. 052 */ 053 public BisectionSolver(double relativeAccuracy, 054 double absoluteAccuracy) { 055 super(relativeAccuracy, absoluteAccuracy); 056 } 057 058 /** 059 * {@inheritDoc} 060 */ 061 @Override 062 protected double doSolve() 063 throws TooManyEvaluationsException { 064 double min = getMin(); 065 double max = getMax(); 066 verifyInterval(min, max); 067 final double absoluteAccuracy = getAbsoluteAccuracy(); 068 double m; 069 double fm; 070 double fmin; 071 072 while (true) { 073 m = UnivariateSolverUtils.midpoint(min, max); 074 fmin = computeObjectiveValue(min); 075 fm = computeObjectiveValue(m); 076 077 if (fm * fmin > 0) { 078 // max and m bracket the root. 079 min = m; 080 } else { 081 // min and m bracket the root. 082 max = m; 083 } 084 085 if (FastMath.abs(max - min) <= absoluteAccuracy) { 086 m = UnivariateSolverUtils.midpoint(min, max); 087 return m; 088 } 089 } 090 } 091}