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Diffstat (limited to '.venv/lib/python3.12/site-packages/networkx/algorithms/components/semiconnected.py')
-rw-r--r-- | .venv/lib/python3.12/site-packages/networkx/algorithms/components/semiconnected.py | 71 |
1 files changed, 71 insertions, 0 deletions
diff --git a/.venv/lib/python3.12/site-packages/networkx/algorithms/components/semiconnected.py b/.venv/lib/python3.12/site-packages/networkx/algorithms/components/semiconnected.py new file mode 100644 index 00000000..9ca5d762 --- /dev/null +++ b/.venv/lib/python3.12/site-packages/networkx/algorithms/components/semiconnected.py @@ -0,0 +1,71 @@ +"""Semiconnectedness.""" + +import networkx as nx +from networkx.utils import not_implemented_for, pairwise + +__all__ = ["is_semiconnected"] + + +@not_implemented_for("undirected") +@nx._dispatchable +def is_semiconnected(G): + r"""Returns True if the graph is semiconnected, False otherwise. + + A graph is semiconnected if and only if for any pair of nodes, either one + is reachable from the other, or they are mutually reachable. + + This function uses a theorem that states that a DAG is semiconnected + if for any topological sort, for node $v_n$ in that sort, there is an + edge $(v_i, v_{i+1})$. That allows us to check if a non-DAG `G` is + semiconnected by condensing the graph: i.e. constructing a new graph `H` + with nodes being the strongly connected components of `G`, and edges + (scc_1, scc_2) if there is a edge $(v_1, v_2)$ in `G` for some + $v_1 \in scc_1$ and $v_2 \in scc_2$. That results in a DAG, so we compute + the topological sort of `H` and check if for every $n$ there is an edge + $(scc_n, scc_{n+1})$. + + Parameters + ---------- + G : NetworkX graph + A directed graph. + + Returns + ------- + semiconnected : bool + True if the graph is semiconnected, False otherwise. + + Raises + ------ + NetworkXNotImplemented + If the input graph is undirected. + + NetworkXPointlessConcept + If the graph is empty. + + Examples + -------- + >>> G = nx.path_graph(4, create_using=nx.DiGraph()) + >>> print(nx.is_semiconnected(G)) + True + >>> G = nx.DiGraph([(1, 2), (3, 2)]) + >>> print(nx.is_semiconnected(G)) + False + + See Also + -------- + is_strongly_connected + is_weakly_connected + is_connected + is_biconnected + """ + if len(G) == 0: + raise nx.NetworkXPointlessConcept( + "Connectivity is undefined for the null graph." + ) + + if not nx.is_weakly_connected(G): + return False + + H = nx.condensation(G) + + return all(H.has_edge(u, v) for u, v in pairwise(nx.topological_sort(H))) |