Class ContractionHierarchyBidirectionalDijkstra<V,E>
 Type Parameters:
V
 the graph vertex typeE
 the graph edge type
 All Implemented Interfaces:
ShortestPathAlgorithm<V,
E>
The query algorithm is originally described the article: Robert Geisberger, Peter Sanders, Dominik Schultes, and Daniel Delling. 2008. Contraction hierarchies: faster and simpler hierarchical routing in road networks. In Proceedings of the 7th international conference on Experimental algorithms (WEA'08), Catherine C. McGeoch (Ed.). SpringerVerlag, Berlin, Heidelberg, 319333.
During contraction graph is divided into 2 parts which are called upward and downward graphs. Both parts have all vertices of the original graph. The upward graph ($G_{\uparrow}$) contains only those edges which source has lower level than the target and vice versa for the downward graph ($G_{\downarrow}$).
For the shortest path query from $s$ to $t$, a modified bidirectional Dijkstra shortest path search is performed. The forward search from $s$ operates on $G_{\uparrow}$ and the backward search from $t$  on the $G_{\downarrow}$. In each direction only the edges of the corresponding part of the graph are considered. Both searches eventually meet at the vertex $v$, which has the highest level in the shortest path from $s$ to $t$. Whenever a search in one direction reaches a vertex that has already been processed in other direction, a new candidate for a shortest path is found. Search is aborted in one direction if the smallest element in the corresponding priority queue is at least as large as the best candidate path found so far.
After computing a contracted path, the algorithm unpacks it recursively into the actual shortest path using the bypassed edges stored in the contraction hierarchy graph.
There is a possibility to provide an already computed contraction for the graph. For now there is no means to ensure that the specified contraction is correct, nor to failfast. If algorithm uses an incorrect contraction, the results of the search are unpredictable.
Comparing to usual shortest path algorithm, as DijkstraShortestPath
,
AStarShortestPath
, etc., this algorithm spends time for computing contraction hierarchy
but offers significant speedup in shortest path query performance. Therefore it is efficient to
use it in order to compute many shortest path on a single graph. Furthermore, on small graphs
(i.e with less than 1.000 vertices) the overhead of precomputation is higher than the speed at
the stage of computing shortest paths. Typically this algorithm is used to gain speedup for
shortest path queries on graphs of middle and large size (i.e. starting at 1.000 vertices). If a
further query performance improvement is needed take a look at
TransitNodeRoutingShortestPath
.
 Since:
 July 2019
 Author:
 Semen Chudakov
 See Also:

Nested Class Summary
Nested classes/interfaces inherited from interface org.jgrapht.alg.interfaces.ShortestPathAlgorithm
ShortestPathAlgorithm.SingleSourcePaths<V,
E> 
Field Summary
Modifier and TypeFieldDescriptionThe underlying graph.protected static final String
Error message for reporting the existence of a negativeweight cycle.protected static final String
Error message for reporting that a sink vertex is missing.protected static final String
Error message for reporting that a source vertex is missing. 
Constructor Summary
ConstructorDescriptionContractionHierarchyBidirectionalDijkstra
(ContractionHierarchyPrecomputation.ContractionHierarchy<V, E> hierarchy) Constructs a new instance of the algorithm for a givenhierarchy
.ContractionHierarchyBidirectionalDijkstra
(ContractionHierarchyPrecomputation.ContractionHierarchy<V, E> hierarchy, double radius, Supplier<org.jheaps.AddressableHeap<Double, Pair<ContractionHierarchyPrecomputation.ContractionVertex<V>, ContractionHierarchyPrecomputation.ContractionEdge<E>>>> heapSupplier) Constructs a new instance of the algorithm for the givenhierarchy
,radius
andheapSupplier
.ContractionHierarchyBidirectionalDijkstra
(Graph<V, E> graph, ThreadPoolExecutor executor) Constructs a new instance of the algorithm for a givengraph
andexecutor
. 
Method Summary
Modifier and TypeMethodDescriptioncreateEmptyPath
(V source, V sink) Create an empty path.Get a shortest path from a source vertex to a sink vertex.Compute all shortest paths starting from a single source vertex.double
getPathWeight
(V source, V sink) Get the weight of the shortest path from a source vertex to a sink vertex.

Field Details

GRAPH_CONTAINS_A_NEGATIVE_WEIGHT_CYCLE
Error message for reporting the existence of a negativeweight cycle. See Also:

GRAPH_MUST_CONTAIN_THE_SOURCE_VERTEX
Error message for reporting that a source vertex is missing. See Also:

GRAPH_MUST_CONTAIN_THE_SINK_VERTEX
Error message for reporting that a sink vertex is missing. See Also:

graph
The underlying graph.


Constructor Details

ContractionHierarchyBidirectionalDijkstra
Constructs a new instance of the algorithm for a givengraph
andexecutor
. It is up to a user of this algorithm to handle the creation and termination of the providedexecutor
. For utility methods to manage aThreadPoolExecutor
seeConcurrencyUtil
. Parameters:
graph
 the graphexecutor
 executor which is used for computing theContractionHierarchyPrecomputation.ContractionHierarchy

ContractionHierarchyBidirectionalDijkstra
public ContractionHierarchyBidirectionalDijkstra(ContractionHierarchyPrecomputation.ContractionHierarchy<V, E> hierarchy) Constructs a new instance of the algorithm for a givenhierarchy
. Parameters:
hierarchy
 contraction of thegraph

ContractionHierarchyBidirectionalDijkstra
public ContractionHierarchyBidirectionalDijkstra(ContractionHierarchyPrecomputation.ContractionHierarchy<V, E> hierarchy, double radius, Supplier<org.jheaps.AddressableHeap<Double, Pair<ContractionHierarchyPrecomputation.ContractionVertex<V>, ContractionHierarchyPrecomputation.ContractionEdge<E>>>> heapSupplier) Constructs a new instance of the algorithm for the givenhierarchy
,radius
andheapSupplier
. Parameters:
hierarchy
 contraction of thegraph
radius
 search radiusheapSupplier
 supplier of the preferable heap implementation


Method Details

getPath
Get a shortest path from a source vertex to a sink vertex. Parameters:
source
 the source vertexsink
 the target vertex Returns:
 a shortest path or null if no path exists

getPaths
Compute all shortest paths starting from a single source vertex. Specified by:
getPaths
in interfaceShortestPathAlgorithm<V,
E>  Parameters:
source
 the source vertex Returns:
 the shortest paths

getPathWeight
Get the weight of the shortest path from a source vertex to a sink vertex. ReturnsDouble.POSITIVE_INFINITY
if no path exists. Specified by:
getPathWeight
in interfaceShortestPathAlgorithm<V,
E>  Parameters:
source
 the source vertexsink
 the sink vertex Returns:
 the weight of the shortest path from a source vertex to a sink vertex, or
Double.POSITIVE_INFINITY
if no path exists

createEmptyPath
Create an empty path. Returns null if the source vertex is different than the target vertex. Parameters:
source
 the source vertexsink
 the sink vertex Returns:
 an empty path or null null if the source vertex is different than the target vertex
