| /* |
| * Copyright 2004 The Apache Software Foundation. |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package org.apache.commons.math.analysis; |
| |
| import org.apache.commons.math.ConvergenceException; |
| import org.apache.commons.math.FunctionEvaluationException; |
| |
| /** |
| * Implements <a href="http://mathworld.wolfram.com/NewtonsMethod.html"> |
| * Newton's Method</a> for finding zeros of real univariate functions. |
| * <p> |
| * The function should be continuous but not necessarily smooth. |
| * |
| * @version $Revision$ $Date$ |
| */ |
| public class NewtonSolver extends UnivariateRealSolverImpl { |
| |
| /** Serializable version identifier */ |
| static final long serialVersionUID = 2606474895443431607L; |
| |
| /** The first derivative of the target function. */ |
| private UnivariateRealFunction derivative; |
| |
| /** |
| * Construct a solver for the given function. |
| * @param f function to solve. |
| */ |
| public NewtonSolver(DifferentiableUnivariateRealFunction f) { |
| super(f, 100, 1E-6); |
| derivative = f.derivative(); |
| } |
| |
| /** |
| * Find a zero near the midpoint of <code>min</code> and <code>max</code>. |
| * |
| * @param min the lower bound for the interval |
| * @param max the upper bound for the interval |
| * @return the value where the function is zero |
| * @throws ConvergenceException if the maximum iteration count is exceeded |
| * @throws FunctionEvaluationException if an error occurs evaluating the |
| * function or derivative |
| * @throws IllegalArgumentException if min is not less than max |
| */ |
| public double solve(double min, double max) throws ConvergenceException, |
| FunctionEvaluationException { |
| return solve(min, max, UnivariateRealSolverUtils.midpoint(min, max)); |
| } |
| |
| /** |
| * Find a zero near the value <code>startValue</code>. |
| * |
| * @param min the lower bound for the interval (ignored). |
| * @param max the upper bound for the interval (ignored). |
| * @param startValue the start value to use. |
| * @return the value where the function is zero |
| * @throws ConvergenceException if the maximum iteration count is exceeded |
| * @throws FunctionEvaluationException if an error occurs evaluating the |
| * function or derivative |
| * @throws IllegalArgumentException if startValue is not between min and max |
| */ |
| public double solve(double min, double max, double startValue) |
| throws ConvergenceException, FunctionEvaluationException { |
| |
| clearResult(); |
| verifySequence(min, startValue, max); |
| |
| double x0 = startValue; |
| double x1; |
| |
| int i = 0; |
| while (i < maximalIterationCount) { |
| x1 = x0 - (f.value(x0) / derivative.value(x0)); |
| if (Math.abs(x1 - x0) <= absoluteAccuracy) { |
| |
| setResult(x1, i); |
| return x1; |
| } |
| |
| x0 = x1; |
| ++i; |
| } |
| |
| throw new ConvergenceException |
| ("Maximum number of iterations exceeded " + i); |
| } |
| |
| } |