# diameter#

diameter(G, seed=None)[source]#

Returns a lower bound on the diameter of the graph G.

The function computes a lower bound on the diameter (i.e., the maximum eccentricity) of a directed or undirected graph G. The procedure used varies depending on the graph being directed or not.

If G is an undirected graph, then the function uses the 2-sweep algorithm [1]. The main idea is to pick the farthest node from a random node and return its eccentricity.

Otherwise, if G is a directed graph, the function uses the 2-dSweep algorithm [2], The procedure starts by selecting a random source node $$s$$ from which it performs a forward and a backward BFS. Let $$a_1$$ and $$a_2$$ be the farthest nodes in the forward and backward cases, respectively. Then, it computes the backward eccentricity of $$a_1$$ using a backward BFS and the forward eccentricity of $$a_2$$ using a forward BFS. Finally, it returns the best lower bound between the two.

In both cases, the time complexity is linear with respect to the size of G.

Parameters:
GNetworkX graph
seedinteger, random_state, or None (default)

Indicator of random number generation state. See Randomness.

Returns:
dinteger

Lower Bound on the Diameter of G

Raises:
NetworkXError

If the graph is empty or If the graph is undirected and not connected or If the graph is directed and not strongly connected.

References

[1]

Magnien, Clémence, Matthieu Latapy, and Michel Habib. Fast computation of empirically tight bounds for the diameter of massive graphs. Journal of Experimental Algorithmics (JEA), 2009. https://arxiv.org/pdf/0904.2728.pdf

[2]

Crescenzi, Pierluigi, Roberto Grossi, Leonardo Lanzi, and Andrea Marino. On computing the diameter of real-world directed (weighted) graphs. International Symposium on Experimental Algorithms. Springer, Berlin, Heidelberg, 2012. https://courses.cs.ut.ee/MTAT.03.238/2014_fall/uploads/Main/diameter.pdf

Examples

>>> G = nx.path_graph(10)  # undirected graph
>>> nx.diameter(G)
9
>>> G = nx.cycle_graph(3, create_using=nx.DiGraph)  # directed graph
>>> nx.diameter(G)
2