org.jgrapht.alg.BellmanFordPathElement Maven / Gradle / Ivy
/* ==========================================
* JGraphT : a free Java graph-theory library
* ==========================================
*
* Project Info: http://jgrapht.sourceforge.net/
* Project Creator: Barak Naveh (http://sourceforge.net/users/barak_naveh)
*
* (C) Copyright 2003-2008, by Barak Naveh and Contributors.
*
* This program and the accompanying materials are dual-licensed under
* either
*
* (a) the terms of the GNU Lesser General Public License version 2.1
* as published by the Free Software Foundation, or (at your option) any
* later version.
*
* or (per the licensee's choosing)
*
* (b) the terms of the Eclipse Public License v1.0 as published by
* the Eclipse Foundation.
*/
/* -------------------------
* BellmanFordPathElement.java
* -------------------------
* (C) Copyright 2006-2008, by France Telecom and Contributors.
*
* Original Author: Guillaume Boulmier and Contributors.
* Contributor(s): John V. Sichi
*
* $Id$
*
* Changes
* -------
* 05-Jan-2006 : Initial revision (GB);
* 14-Jan-2006 : Added support for generics (JVS);
*
*/
package org.jgrapht.alg;
import org.jgrapht.*;
/**
* Helper class for {@link BellmanFordShortestPath}; not intended for general
* use.
*/
final class BellmanFordPathElement
extends AbstractPathElement
{
private double cost = 0;
private double epsilon;
/**
* Creates a path element by concatenation of an edge to a path element.
*
* @param pathElement
* @param edge edge reaching the end vertex of the path element created.
* @param cost total cost of the created path element.
* @param epsilon tolerance factor.
*/
protected BellmanFordPathElement(
Graph graph,
BellmanFordPathElement pathElement,
E edge,
double cost,
double epsilon)
{
super(graph, pathElement, edge);
this.cost = cost;
this.epsilon = epsilon;
}
/**
* Copy constructor.
*
* @param original source to copy from
*/
BellmanFordPathElement(BellmanFordPathElement original)
{
super(original);
this.cost = original.cost;
this.epsilon = original.epsilon;
}
/**
* Creates an empty path element.
*
* @param vertex end vertex of the path element.
* @param epsilon tolerance factor.
*/
protected BellmanFordPathElement(V vertex, double epsilon)
{
super(vertex);
this.cost = 0;
this.epsilon = epsilon;
}
/**
* Returns the total cost of the path element.
*
* @return .
*/
public double getCost()
{
return this.cost;
}
/**
* Returns true if the path has been improved,
* false otherwise. We use an "epsilon" precision to check whether
* the cost has been improved (because of many roundings, a formula equal to
* 0 could unfortunately be evaluated to 10^-14).
*
* @param candidatePrevPathElement
* @param candidateEdge
* @param candidateCost
*
* @return .
*/
protected boolean improve(
BellmanFordPathElement candidatePrevPathElement,
E candidateEdge,
double candidateCost)
{
// to avoid improvement only due to rounding errors.
if (candidateCost < (getCost() - epsilon)) {
this.prevPathElement = candidatePrevPathElement;
this.prevEdge = candidateEdge;
this.cost = candidateCost;
this.nHops = candidatePrevPathElement.getHopCount() + 1;
return true;
} else {
return false;
}
}
}
// End BellmanFordPathElement.java