Note

This is the documentation for the current state of the development branch of rustworkx. The documentation or APIs here can change prior to being released.

# rustworkx.graph_floyd_warshall#

graph_floyd_warshall(graph, /, weight_fn=None, default_weight=1.0, parallel_threshold=300)#

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 (PyGraph) – The graph to run Floyd’s algorithm on

• weight_fn

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:

graph_floyd_warshall(graph, weight_fn= lambda x: 1)

to return a weight of 1 for all edges. Also:

graph_floyd_warshall(graph, weight_fn=float)

to cast the edge object as a float as the weight.

• 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 source node indices and the values are dicts 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