Class DijkstraIterator
 Object

 AbstractGraphIterator

 SourceGraphIterator

 DijkstraIterator

 All Implemented Interfaces:
GraphIterator
 Direct Known Subclasses:
DirectedDijkstraIterator
public class DijkstraIterator extends SourceGraphIterator
Iterates over the nodes of a graph in pattern using Dijkstra's Shortest Path Algorithm. A Dijkstra iteration returns nodes in an order of increasing cost relative to a specified node (the source node of the iteration).
In a Dijkstra iteration, a weight is associated with each edge and a cost with each node. The iteration operates by maintaining two sets of nodes. The first the set of nodes whose final cost is known, and the second is the set of nodes whose final cost is unknown. Initially, every node except for the source node has a cost of infinity, and resides in the unknown set. The source node has a cost of zero, and is is a member of the known set.
The iteration operates as follows:
sn = source node of iteration N = set of all nodes K = set of nodes with known cost = {sn} U = set of nodes with unknown cost = N  K cost(sn) = 0 for each node $un in U cost(un) = infinity while(U > 0) for each node n in K find a node un in U that relates to n if cost(n) + weight(n,un) < cost(un) cost(un) = cost(n) + weight(n,un) ln = node with least cost in U remove ln from U add ln to K return ln as next node in iteration
The following is an illustration of the algorithm. Edge weights are labelled in blue and the final node costs are labelled in red.
The nodes are returned in order of increasing cost which yields the sequence A,C,B,D,E,F,G,H,I. Author:
 Justin Deoliveira, Refractions Research Inc, jdeolive@refractions.net


Nested Class Summary
Nested Classes Modifier and Type Class Description protected static class
DijkstraIterator.DijkstraNode
Internal data structure used to track node costs, and parent nodes.static interface
DijkstraIterator.EdgeWeighter
Supplies a weight for each edge in the graph to be used by the iteration when calculating node costs.static interface
DijkstraIterator.NodeWeighter
Supplies a weight for each pair of adjacent edges.

Field Summary
Fields Modifier and Type Field Description protected HashMap<Graphable,DijkstraIterator.DijkstraNode>
nodemap
map of graph node to internal Dijkstra node *protected DijkstraIterator.NodeWeighter
nweighter
provides weights for nodes in the graph *protected PriorityQueue<DijkstraIterator.DijkstraNode>
queue
priority queue to manage active nodes *protected DijkstraIterator.EdgeWeighter
weighter
provides weights for edges in the graph *

Constructor Summary
Constructors Constructor Description DijkstraIterator(DijkstraIterator.EdgeWeighter weighter)
Constructs a new Dijkstra iterator which uses the specified EdgeWeighter.DijkstraIterator(DijkstraIterator.EdgeWeighter weighter, DijkstraIterator.NodeWeighter nweighter)
Constructs a new Dijkstra iterator which uses the specified EdgeWeighter and NodeWeighter

Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description void
cont(Graphable current, GraphTraversal traversal)
Looks for adjacent nodes to the current node which are in the adjacent node and updates costs.double
getCost(Graphable component)
Returns the internal cost of a node which has been calculated by the iterator.Graphable
getParent(Graphable component)
Returns the last node in the known set to update the node.protected PriorityQueue
getQueue()
protected Iterator<? extends Graphable>
getRelated(Graphable current)
void
init(Graph graph, GraphTraversal traversal)
Builds internal priority queue to manage node costs.void
killBranch(Graphable current, GraphTraversal traversal)
Kills the branch of the traversal by not updating the cost of any adjacent nodes.Graphable
next(GraphTraversal traversal)
Returns the next node in the priority queue.
Methods inherited from class SourceGraphIterator
getSource, setSource

Methods inherited from class AbstractGraphIterator
getGraph, getTraversal, getWalker, setTraversal




Field Detail

weighter
protected DijkstraIterator.EdgeWeighter weighter
provides weights for edges in the graph *

nweighter
protected DijkstraIterator.NodeWeighter nweighter
provides weights for nodes in the graph *

queue
protected PriorityQueue<DijkstraIterator.DijkstraNode> queue
priority queue to manage active nodes *

nodemap
protected HashMap<Graphable,DijkstraIterator.DijkstraNode> nodemap
map of graph node to internal Dijkstra node *


Constructor Detail

DijkstraIterator
public DijkstraIterator(DijkstraIterator.EdgeWeighter weighter)
Constructs a new Dijkstra iterator which uses the specified EdgeWeighter. Parameters:
weighter
 Calculates weights for edges in the graph being iterated over.

DijkstraIterator
public DijkstraIterator(DijkstraIterator.EdgeWeighter weighter, DijkstraIterator.NodeWeighter nweighter)
Constructs a new Dijkstra iterator which uses the specified EdgeWeighter and NodeWeighter Parameters:
weighter
 Calculates weights for edges in the graph being iterated over.nweighter
 Calculates weights for nodes in the graph being iterated over.


Method Detail

init
public void init(Graph graph, GraphTraversal traversal)
Builds internal priority queue to manage node costs. Parameters:
graph
 The graph being whose components are being iterated over. See Also:
org.geotools.graph.traverse.GraphIterator#init(Graph)

next
public Graphable next(GraphTraversal traversal)
Returns the next node in the priority queue. If the next node coming out of the queue has infinite cost, then the node is not adjacent to any nodes in the set of nodes with known costs. This situation will end the traversal every other node will also have infinite cost. This usually is the result of a disconnected graph. Returns:
 The next component in the iteration, or null if iteration is complete.
 See Also:
org.geotools.graph.traverse.GraphIterator#next()

cont
public void cont(Graphable current, GraphTraversal traversal)
Looks for adjacent nodes to the current node which are in the adjacent node and updates costs. Parameters:
current
 The current component of the traversal. See Also:
org.geotools.graph.traverse.GraphIterator#cont(Graphable)

killBranch
public void killBranch(Graphable current, GraphTraversal traversal)
Kills the branch of the traversal by not updating the cost of any adjacent nodes. Parameters:
current
 The current component of the traversal. See Also:
org.geotools.graph.traverse.GraphIterator#killBranch(Graphable)

getCost
public double getCost(Graphable component)
Returns the internal cost of a node which has been calculated by the iterator. Parameters:
component
 The component whose cost to return. Returns:
 The cost associated with the component.

getParent
public Graphable getParent(Graphable component)
Returns the last node in the known set to update the node. The iteration operates by nodes in the known set updating the cost of nodes in the unknown set. Each time an update occurs, the known node is set as the parent of the unkown node. Parameters:
component
 The node whose parent to return (child) Returns:
 The parent, or null if the method is supplied the source of the iteration.

getQueue
protected PriorityQueue getQueue()

