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/* ==========================================
* 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 2003-2007, by Barak Naveh and Contributors.
*
* This library is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2.1 of the License, or
* (at your option) any later version.
*
* This library is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this library; if not, write to the Free Software Foundation,
* Inc.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
*/
/* -------------------------
* BellmanFordPathElement.java
* -------------------------
* (C) Copyright 2006-2007, by France Telecom and Contributors.
*
* Original Author: Guillaume Boulmier and Contributors.
* Contributor(s): John V. Sichi
*
* $Id: BellmanFordPathElement.java 568 2007-09-30 00:12:18Z perfecthash $
*
* 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
{
//~ Instance fields --------------------------------------------------------
private double cost = 0;
private double epsilon;
//~ Constructors -----------------------------------------------------------
/**
* 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;
}
//~ Methods ----------------------------------------------------------------
/**
* 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