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# single_pair_shortest_path_bellman_ford(+Graph, +DistanceArg, +SourceNode, +SinkNode, -Path)

Computes one shortest path from a source to a sink node (allowing negative distances)
*Graph*
- a graph structure
*DistanceArg*
- which argument of EdgeData to use as distance: integer
*SourceNode*
- source node number
*SinkNode*
- sink node number
*Path*
- Length-EdgeList structure

## Description

Computes one shortest path from SourceNode to SinkNode.
Fails if there is no path at all. In case of multiple
shortest paths with the same length, an arbitrary one is returned.

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. As opposed to the other
shortest path algorithms, the Bellman-Ford algorithm can handle
negative edge lengths, however, the implementation has currently
no check for negative cycles and will not terminate in that case.

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

The shortest path is returned as a Length-EdgeList structure
where Length is the length of the shortest path and EdgeList is that
path (or one of them) in reverse order, i.e. starting with the edge
reaching SinkNode and ending with the edge starting from SourceNode.

### Modes and Determinism

- single_pair_shortest_path_bellman_ford(+, +, +, +, -) is semidet

### Fail Conditions

There is no path from SourceNode to SinkNode
## Examples

?- sample_graph(G), single_pair_shortest_path_bellman_ford(G, 0, 1, 3, P).
P = 2 - [e(2, 3, 1), e(1, 2, 1)]

## See Also

shortest_paths_bellman_ford / 4, single_pair_shortest_path / 5