org.jgrapht.alg

Class AStarShortestPath<V,E>

java.lang.Object

org.jgrapht.alg.AStarShortestPath<V,E>

public class AStarShortestPath<V,E>
extends Object

An implementation of A* shortest path algorithm. A* shortest path algorithm german Wiki . This class works for Directed and Undirected graphs, as well as Multi-Graphs and Mixed-Graphs. It's ok if the graph changes in between invocations of the getShortestPath(Object, Object, AStarAdmissibleHeuristic) getShortestPath} method; no new instance of this class has to be created. The heuristic is implemented using a FibonacciHeap data structure to maintain the set of open nodes. However, there still exist several approaches in literature to improve the performance of this heuristic which one could consider to implement. Another issue to take into consideration is the following: given to candidate nodes, i, j to expand, where f(i)=f(j), g(i)>g(j), h(i)<g(j), f(i)=g(i)+h(i), g(i) is the actual distance from the source node to i, h(i) is the estimated distance from i to the target node. Usually a depth-first search is desired, so ideally we would expand node i first. Using the FibonacciHeap, this is not necessarily the case though. This could be improved in a later version.

Since:

Aug, 2015

Author:

Joris Kinable, Jon Robison, Thomas Breitbart

Field Summary

Fields

Modifier and Type	Field and Description
protected AStarAdmissibleHeuristic<V>	admissibleHeuristic
protected Map<V,E>	cameFrom
protected Set<V>	closedList
protected Map<V,Double>	gScoreMap
protected int	numberOfExpandedNodes
protected FibonacciHeap<V>	openList
protected Map<V,FibonacciHeapNode<V>>	vertexToHeapNodeMap

Constructor Summary

Constructors

Constructor and Description
AStarShortestPath(Graph<V,E> graph)

Method Summary

Methods

Modifier and Type	Method and Description
int	getNumberOfExpandedNodes() Returns how many nodes have been expanded in the A* search procedure in its last invocation.
GraphPath<V,E>	getShortestPath(V sourceVertex, V targetVertex, AStarAdmissibleHeuristic<V> admissibleHeuristic) Calculates (and returns) the shortest path from the sourceVertex to the targetVertex.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

openList

protected FibonacciHeap<V> openList

vertexToHeapNodeMap

protected Map<V,FibonacciHeapNode<V>> vertexToHeapNodeMap

closedList

protected Set<V> closedList

gScoreMap

protected Map<V,Double> gScoreMap

cameFrom

protected Map<V,E> cameFrom

admissibleHeuristic

protected AStarAdmissibleHeuristic<V> admissibleHeuristic

numberOfExpandedNodes

protected int numberOfExpandedNodes

Constructor Detail

AStarShortestPath

public AStarShortestPath(Graph<V,E> graph)

Method Detail

getShortestPath

public GraphPath<V,E> getShortestPath(V sourceVertex,
                             V targetVertex,
                             AStarAdmissibleHeuristic<V> admissibleHeuristic)

Calculates (and returns) the shortest path from the sourceVertex to the targetVertex. Note: each time you invoke this method, the path gets recomputed.

Parameters:

sourceVertex - source vertex

targetVertex - target vertex

admissibleHeuristic - admissible heuristic which estimates the distance from a node to the target node.

Returns:

the shortest path from sourceVertex to targetVertex

getNumberOfExpandedNodes

public int getNumberOfExpandedNodes()

Returns how many nodes have been expanded in the A* search procedure in its last invocation. A node is expanded if it is removed from the open list.

Returns:

number of expanded nodes