org.jgrapht.alg

Class AStarShortestPath<V,E>

java.lang.Object

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

Type Parameters:

V - the graph vertex type

E - the graph edge type

Deprecated.

in favor of AStarShortestPath

@Deprecated
public class AStarShortestPath<V,E>
extends java.lang.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 two 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.

Note: This implementation works with both consistent and inconsistent admissible heuristics. For details on consistency, refer to the description of the method isConsistentHeuristic(AStarAdmissibleHeuristic). However, this class is not optimized for inconsistent heuristics. Several opportunities to improve both worst case and average runtime complexities for A* with inconsistent heuristics described in literature can be used to improve this implementation!

Since:

Aug, 2015

Constructor Summary

Constructors

Constructor and Description
AStarShortestPath(Graph<V,E> graph) Deprecated. Create a new instance of the A* shortest path algorithm.

Method Summary

Modifier and Type	Method and Description
int	getNumberOfExpandedNodes() Deprecated. 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) Deprecated. Calculates (and returns) the shortest path from the sourceVertex to the targetVertex.
boolean	isConsistentHeuristic(AStarAdmissibleHeuristic<V> admissibleHeuristic) Deprecated. Returns true if the provided heuristic is a consistent or monotone heuristic wrt the graph provided at construction time.

Methods inherited from class java.lang.Object

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

Constructor Detail

AStarShortestPath

public AStarShortestPath(Graph<V,E> graph)

Deprecated.

Create a new instance of the A* shortest path algorithm.

Parameters:

graph - the input graph

Method Detail

getShortestPath

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

Deprecated.

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()

Deprecated.

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

isConsistentHeuristic

public boolean isConsistentHeuristic(AStarAdmissibleHeuristic<V> admissibleHeuristic)

Deprecated.

Returns true if the provided heuristic is a consistent or monotone heuristic wrt the graph provided at construction time. A heuristic is monotonic if its estimate is always less than or equal to the estimated distance from any neighboring vertex to the goal, plus the step cost of reaching that neighbor. For details, refer to https://en.wikipedia.org/wiki/Consistent_heuristic. In short, a heuristic is consistent iff h(u)≤ d(u,v)+h(v), for every edge (u,v), where d(u,v) is the weight of edge (u,v) and h(u) is the estimated cost to reach the target node from vertex u. Most natural admissible heuristics, such as Manhattan or Euclidian distance, are consistent heuristics.

Parameters:

admissibleHeuristic - admissible heuristic

Returns:

true is the heuristic is consistent