two version of R2R are here HEAD master

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
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+++ b/.venv/lib/python3.12/site-packages/networkx/algorithms/components/semiconnected.py
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+"""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)))