PegasusSolver.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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,
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 * See the License for the specific language governing permissions and
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package org.apache.commons.math4.legacy.analysis.solvers;

/**
 * Implements the <em>Pegasus</em> method for root-finding (approximating
 * a zero of a univariate real function). It is a modified
 * {@link RegulaFalsiSolver <em>Regula Falsi</em>} method.
 *
 * <p>Like the <em>Regula Falsi</em> method, convergence is guaranteed by
 * maintaining a bracketed solution. The <em>Pegasus</em> method however,
 * should converge much faster than the original <em>Regula Falsi</em>
 * method. Furthermore, this implementation of the <em>Pegasus</em> method
 * should not suffer from the same implementation issues as the <em>Regula
 * Falsi</em> method, which may fail to convergence in certain cases. Also,
 * the <em>Pegasus</em> method should converge faster than the
 * {@link IllinoisSolver <em>Illinois</em>} method, another <em>Regula
 * Falsi</em>-based method.</p>
 *
 * <p>The <em>Pegasus</em> method assumes that the function is continuous,
 * but not necessarily smooth.</p>
 *
 * <p>Implementation based on the following article: M. Dowell and P. Jarratt,
 * <em>The "Pegasus" method for computing the root of an equation</em>,
 * BIT Numerical Mathematics, volume 12, number 4, pages 503-508, Springer,
 * 1972.</p>
 *
 * @since 3.0
 */
public class PegasusSolver extends BaseSecantSolver {

    /** Construct a solver with default accuracy (1e-6). */
    public PegasusSolver() {
        super(DEFAULT_ABSOLUTE_ACCURACY, Method.PEGASUS);
    }

    /**
     * Construct a solver.
     *
     * @param absoluteAccuracy Absolute accuracy.
     */
    public PegasusSolver(final double absoluteAccuracy) {
        super(absoluteAccuracy, Method.PEGASUS);
    }

    /**
     * Construct a solver.
     *
     * @param relativeAccuracy Relative accuracy.
     * @param absoluteAccuracy Absolute accuracy.
     */
    public PegasusSolver(final double relativeAccuracy,
                         final double absoluteAccuracy) {
        super(relativeAccuracy, absoluteAccuracy, Method.PEGASUS);
    }

    /**
     * Construct a solver.
     *
     * @param relativeAccuracy Relative accuracy.
     * @param absoluteAccuracy Absolute accuracy.
     * @param functionValueAccuracy Maximum function value error.
     */
    public PegasusSolver(final double relativeAccuracy,
                         final double absoluteAccuracy,
                         final double functionValueAccuracy) {
        super(relativeAccuracy, absoluteAccuracy, functionValueAccuracy, Method.PEGASUS);
    }
}