rustworkx.floyd_warshall#

floyd_warshall(graph, weight_fn=None, default_weight=1.0, parallel_threshold=300)[source]#

Find all-pairs shortest path lengths using Floyd’s algorithm

Floyd’s algorithm is used for finding shortest paths in dense graphs or graphs with negative weights (where Dijkstra’s algorithm fails).

This function is multithreaded and will launch a pool with threads equal to the number of CPUs by default if the number of nodes in the graph is above the value of parallel_threshold (it defaults to 300). You can tune the number of threads with the RAYON_NUM_THREADS environment variable. For example, setting RAYON_NUM_THREADS=4 would limit the thread pool to 4 threads if parallelization was enabled.

Parameters:

graph – The graph to run Floyd’s algorithm on. Can either be a PyGraph or PyDiGraph
weight_fn (callable) –
A callable object (function, lambda, etc) which will be passed the edge object and expected to return a float. This tells rustworkx/rust how to extract a numerical weight as a float for edge object. Some simple examples are:
```
floyd_warshall(graph, weight_fn= lambda x: 1)
```
to return a weight of 1 for all edges. Also:
```
floyd_warshall(graph, weight_fn=float)
```
to cast the edge object as a float as the weight. If this is not specified a default value (either default_weight or 1) will be used for all edges.
default_weight (float) – If weight_fn is not used this can be optionally used to specify a default weight to use for all edges.
parallel_threshold (int) – The number of nodes to execute the algorithm in parallel at. It defaults to 300, but this can be tuned

Returns:

A read-only dictionary of path lengths. The keys are the source node indices and the values are a dict of the target node and the length of the shortest path to that node. For example:

{
    0: {0: 0.0, 1: 2.0, 2: 2.0},
    1: {1: 0.0, 2: 1.0},
    2: {0: 1.0, 2: 0.0},
}

Return type:

AllPairsPathLengthMapping