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incremental_single_pair_all_shortest_paths_as_graph(+Graph, +DistanceArg, +SourceNode, +SinkNode, +Modified, -Length, -SubGraph)

Computes all shortest paths from source to sink in form of a subgraph
Graph
a graph structure
DistanceArg
which argument of EdgeData to use as distance (integer)
SourceNode
source node number (integer)
SinkNode
sink node number (integer)
Modified
list of e/3 edge structures whose DistanceArg argument has been modified
Length
a number (minimum path length)
SubGraph
a graph structure

Description

Incrementally computes all shortest paths from source node SourceNode to sink node SinkNode. The result is returned in the form of a sub-graph of the input graph, which contains all relevant edges. If there is no path, the predicate fails.

DistanceArg refers to the graph's EdgeData information that was specified when the graph was constructed. If EdgeData is a simple number, then DistanceArg should be 0 and EdgeData will be taken as the length of the edge. If EdgeData is a compound data structure, DistanceArg should be a number between 1 and the arity of that structure and determines which argument of the EdgeData structure will be interpreted as the edge's length. Important: the distance information in EdgeData must be a non-negative number.

If DistanceArg is given as -1, then any EdgeData is ignored and the length of every edge is assumed to be equal to 1.

Modified is the list of e/3 edge structures whose DistanceArg argument has been modified since the last computation for this SourceNode.

The result is returned in the form of SubGraph, which is a sub-graph of the input Graph, containing the same nodes, but only those edges that are needed to construct the shortest paths for the given parameters. SubGraph does not inherit the nodename information from Graph, this can be set explicitly if required.

In addition, the Length of the shortest path from source to sink is returned.

Properties of the resulting SubGraph

To generate an actual path from the resulting SubGraph, start from the sink node J, select one of its incoming edges (graph_get_incoming_edges/3) to find a predecessor node, and continue this process until the SourceNode is reached. Depending on the input graph, the following 2 cases can occur:

  1. Graph did not contain zero-length edges: in this case, SubGraph is cycle-free and shortest paths can be found by simply selecting arbitrary incoming edges until SourceNode is reached.
  2. Graph did contain zero-length edges: in this case, SubGraph may contain (zero-length) cycles which one may want to exclude when constructing paths.

Modes and Determinism

Examples

    ?- sample_graph(G),
       incremental_single_pair_all_shortest_paths_as_graph(G, 0, 1, 5, M, L, E).
    G = graph(13, []([e(1, 6, 1), e(1, 2, 1), e(1, 7, 1)], [], ...)
    L = 2
    SG = graph(13, []([e(1, 6, 1), e(1, 7, 1)], [], ...)
    

See Also

possible_path / 7, shortest_paths / 4, single_pair_shortest_path / 5, all_short_paths_as_edges / 6, all_short_paths_as_graph / 6, single_pair_short_path / 6, graph_get_incoming_edges / 3, graph_set_nodenames / 2