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Diffstat (limited to '.venv/lib/python3.12/site-packages/networkx/algorithms/connectivity/utils.py')
-rw-r--r-- | .venv/lib/python3.12/site-packages/networkx/algorithms/connectivity/utils.py | 88 |
1 files changed, 88 insertions, 0 deletions
diff --git a/.venv/lib/python3.12/site-packages/networkx/algorithms/connectivity/utils.py b/.venv/lib/python3.12/site-packages/networkx/algorithms/connectivity/utils.py new file mode 100644 index 00000000..7bf99945 --- /dev/null +++ b/.venv/lib/python3.12/site-packages/networkx/algorithms/connectivity/utils.py @@ -0,0 +1,88 @@ +""" +Utilities for connectivity package +""" + +import networkx as nx + +__all__ = ["build_auxiliary_node_connectivity", "build_auxiliary_edge_connectivity"] + + +@nx._dispatchable(returns_graph=True) +def build_auxiliary_node_connectivity(G): + r"""Creates a directed graph D from an undirected graph G to compute flow + based node connectivity. + + For an undirected graph G having `n` nodes and `m` edges we derive a + directed graph D with `2n` nodes and `2m+n` arcs by replacing each + original node `v` with two nodes `vA`, `vB` linked by an (internal) + arc in D. Then for each edge (`u`, `v`) in G we add two arcs (`uB`, `vA`) + and (`vB`, `uA`) in D. Finally we set the attribute capacity = 1 for each + arc in D [1]_. + + For a directed graph having `n` nodes and `m` arcs we derive a + directed graph D with `2n` nodes and `m+n` arcs by replacing each + original node `v` with two nodes `vA`, `vB` linked by an (internal) + arc (`vA`, `vB`) in D. Then for each arc (`u`, `v`) in G we add one + arc (`uB`, `vA`) in D. Finally we set the attribute capacity = 1 for + each arc in D. + + A dictionary with a mapping between nodes in the original graph and the + auxiliary digraph is stored as a graph attribute: D.graph['mapping']. + + References + ---------- + .. [1] Kammer, Frank and Hanjo Taubig. Graph Connectivity. in Brandes and + Erlebach, 'Network Analysis: Methodological Foundations', Lecture + Notes in Computer Science, Volume 3418, Springer-Verlag, 2005. + https://doi.org/10.1007/978-3-540-31955-9_7 + + """ + directed = G.is_directed() + + mapping = {} + H = nx.DiGraph() + + for i, node in enumerate(G): + mapping[node] = i + H.add_node(f"{i}A", id=node) + H.add_node(f"{i}B", id=node) + H.add_edge(f"{i}A", f"{i}B", capacity=1) + + edges = [] + for source, target in G.edges(): + edges.append((f"{mapping[source]}B", f"{mapping[target]}A")) + if not directed: + edges.append((f"{mapping[target]}B", f"{mapping[source]}A")) + H.add_edges_from(edges, capacity=1) + + # Store mapping as graph attribute + H.graph["mapping"] = mapping + return H + + +@nx._dispatchable(returns_graph=True) +def build_auxiliary_edge_connectivity(G): + """Auxiliary digraph for computing flow based edge connectivity + + If the input graph is undirected, we replace each edge (`u`,`v`) with + two reciprocal arcs (`u`, `v`) and (`v`, `u`) and then we set the attribute + 'capacity' for each arc to 1. If the input graph is directed we simply + add the 'capacity' attribute. Part of algorithm 1 in [1]_ . + + References + ---------- + .. [1] Abdol-Hossein Esfahanian. Connectivity Algorithms. (this is a + chapter, look for the reference of the book). + http://www.cse.msu.edu/~cse835/Papers/Graph_connectivity_revised.pdf + """ + if G.is_directed(): + H = nx.DiGraph() + H.add_nodes_from(G.nodes()) + H.add_edges_from(G.edges(), capacity=1) + return H + else: + H = nx.DiGraph() + H.add_nodes_from(G.nodes()) + for source, target in G.edges(): + H.add_edges_from([(source, target), (target, source)], capacity=1) + return H |