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diff --git a/.venv/lib/python3.12/site-packages/networkx/algorithms/centrality/current_flow_betweenness.py b/.venv/lib/python3.12/site-packages/networkx/algorithms/centrality/current_flow_betweenness.py new file mode 100644 index 00000000..bfde279a --- /dev/null +++ b/.venv/lib/python3.12/site-packages/networkx/algorithms/centrality/current_flow_betweenness.py @@ -0,0 +1,342 @@ +"""Current-flow betweenness centrality measures.""" + +import networkx as nx +from networkx.algorithms.centrality.flow_matrix import ( + CGInverseLaplacian, + FullInverseLaplacian, + SuperLUInverseLaplacian, + flow_matrix_row, +) +from networkx.utils import ( + not_implemented_for, + py_random_state, + reverse_cuthill_mckee_ordering, +) + +__all__ = [ + "current_flow_betweenness_centrality", + "approximate_current_flow_betweenness_centrality", + "edge_current_flow_betweenness_centrality", +] + + +@not_implemented_for("directed") +@py_random_state(7) +@nx._dispatchable(edge_attrs="weight") +def approximate_current_flow_betweenness_centrality( + G, + normalized=True, + weight=None, + dtype=float, + solver="full", + epsilon=0.5, + kmax=10000, + seed=None, +): + r"""Compute the approximate current-flow betweenness centrality for nodes. + + Approximates the current-flow betweenness centrality within absolute + error of epsilon with high probability [1]_. + + + Parameters + ---------- + G : graph + A NetworkX graph + + normalized : bool, optional (default=True) + If True the betweenness values are normalized by 2/[(n-1)(n-2)] where + n is the number of nodes in G. + + weight : string or None, optional (default=None) + Key for edge data used as the edge weight. + If None, then use 1 as each edge weight. + The weight reflects the capacity or the strength of the + edge. + + dtype : data type (float) + Default data type for internal matrices. + Set to np.float32 for lower memory consumption. + + solver : string (default='full') + Type of linear solver to use for computing the flow matrix. + Options are "full" (uses most memory), "lu" (recommended), and + "cg" (uses least memory). + + epsilon: float + Absolute error tolerance. + + kmax: int + Maximum number of sample node pairs to use for approximation. + + seed : integer, random_state, or None (default) + Indicator of random number generation state. + See :ref:`Randomness<randomness>`. + + Returns + ------- + nodes : dictionary + Dictionary of nodes with betweenness centrality as the value. + + See Also + -------- + current_flow_betweenness_centrality + + Notes + ----- + The running time is $O((1/\epsilon^2)m{\sqrt k} \log n)$ + and the space required is $O(m)$ for $n$ nodes and $m$ edges. + + If the edges have a 'weight' attribute they will be used as + weights in this algorithm. Unspecified weights are set to 1. + + References + ---------- + .. [1] Ulrik Brandes and Daniel Fleischer: + Centrality Measures Based on Current Flow. + Proc. 22nd Symp. Theoretical Aspects of Computer Science (STACS '05). + LNCS 3404, pp. 533-544. Springer-Verlag, 2005. + https://doi.org/10.1007/978-3-540-31856-9_44 + """ + import numpy as np + + if not nx.is_connected(G): + raise nx.NetworkXError("Graph not connected.") + solvername = { + "full": FullInverseLaplacian, + "lu": SuperLUInverseLaplacian, + "cg": CGInverseLaplacian, + } + n = G.number_of_nodes() + ordering = list(reverse_cuthill_mckee_ordering(G)) + # make a copy with integer labels according to rcm ordering + # this could be done without a copy if we really wanted to + H = nx.relabel_nodes(G, dict(zip(ordering, range(n)))) + L = nx.laplacian_matrix(H, nodelist=range(n), weight=weight).asformat("csc") + L = L.astype(dtype) + C = solvername[solver](L, dtype=dtype) # initialize solver + betweenness = dict.fromkeys(H, 0.0) + nb = (n - 1.0) * (n - 2.0) # normalization factor + cstar = n * (n - 1) / nb + l = 1 # parameter in approximation, adjustable + k = l * int(np.ceil((cstar / epsilon) ** 2 * np.log(n))) + if k > kmax: + msg = f"Number random pairs k>kmax ({k}>{kmax}) " + raise nx.NetworkXError(msg, "Increase kmax or epsilon") + cstar2k = cstar / (2 * k) + for _ in range(k): + s, t = pair = seed.sample(range(n), 2) + b = np.zeros(n, dtype=dtype) + b[s] = 1 + b[t] = -1 + p = C.solve(b) + for v in H: + if v in pair: + continue + for nbr in H[v]: + w = H[v][nbr].get(weight, 1.0) + betweenness[v] += float(w * np.abs(p[v] - p[nbr]) * cstar2k) + if normalized: + factor = 1.0 + else: + factor = nb / 2.0 + # remap to original node names and "unnormalize" if required + return {ordering[k]: v * factor for k, v in betweenness.items()} + + +@not_implemented_for("directed") +@nx._dispatchable(edge_attrs="weight") +def current_flow_betweenness_centrality( + G, normalized=True, weight=None, dtype=float, solver="full" +): + r"""Compute current-flow betweenness centrality for nodes. + + Current-flow betweenness centrality uses an electrical current + model for information spreading in contrast to betweenness + centrality which uses shortest paths. + + Current-flow betweenness centrality is also known as + random-walk betweenness centrality [2]_. + + Parameters + ---------- + G : graph + A NetworkX graph + + normalized : bool, optional (default=True) + If True the betweenness values are normalized by 2/[(n-1)(n-2)] where + n is the number of nodes in G. + + weight : string or None, optional (default=None) + Key for edge data used as the edge weight. + If None, then use 1 as each edge weight. + The weight reflects the capacity or the strength of the + edge. + + dtype : data type (float) + Default data type for internal matrices. + Set to np.float32 for lower memory consumption. + + solver : string (default='full') + Type of linear solver to use for computing the flow matrix. + Options are "full" (uses most memory), "lu" (recommended), and + "cg" (uses least memory). + + Returns + ------- + nodes : dictionary + Dictionary of nodes with betweenness centrality as the value. + + See Also + -------- + approximate_current_flow_betweenness_centrality + betweenness_centrality + edge_betweenness_centrality + edge_current_flow_betweenness_centrality + + Notes + ----- + Current-flow betweenness can be computed in $O(I(n-1)+mn \log n)$ + time [1]_, where $I(n-1)$ is the time needed to compute the + inverse Laplacian. For a full matrix this is $O(n^3)$ but using + sparse methods you can achieve $O(nm{\sqrt k})$ where $k$ is the + Laplacian matrix condition number. + + The space required is $O(nw)$ where $w$ is the width of the sparse + Laplacian matrix. Worse case is $w=n$ for $O(n^2)$. + + If the edges have a 'weight' attribute they will be used as + weights in this algorithm. Unspecified weights are set to 1. + + References + ---------- + .. [1] Centrality Measures Based on Current Flow. + Ulrik Brandes and Daniel Fleischer, + Proc. 22nd Symp. Theoretical Aspects of Computer Science (STACS '05). + LNCS 3404, pp. 533-544. Springer-Verlag, 2005. + https://doi.org/10.1007/978-3-540-31856-9_44 + + .. [2] A measure of betweenness centrality based on random walks, + M. E. J. Newman, Social Networks 27, 39-54 (2005). + """ + if not nx.is_connected(G): + raise nx.NetworkXError("Graph not connected.") + N = G.number_of_nodes() + ordering = list(reverse_cuthill_mckee_ordering(G)) + # make a copy with integer labels according to rcm ordering + # this could be done without a copy if we really wanted to + H = nx.relabel_nodes(G, dict(zip(ordering, range(N)))) + betweenness = dict.fromkeys(H, 0.0) # b[n]=0 for n in H + for row, (s, t) in flow_matrix_row(H, weight=weight, dtype=dtype, solver=solver): + pos = dict(zip(row.argsort()[::-1], range(N))) + for i in range(N): + betweenness[s] += (i - pos[i]) * row.item(i) + betweenness[t] += (N - i - 1 - pos[i]) * row.item(i) + if normalized: + nb = (N - 1.0) * (N - 2.0) # normalization factor + else: + nb = 2.0 + return {ordering[n]: (b - n) * 2.0 / nb for n, b in betweenness.items()} + + +@not_implemented_for("directed") +@nx._dispatchable(edge_attrs="weight") +def edge_current_flow_betweenness_centrality( + G, normalized=True, weight=None, dtype=float, solver="full" +): + r"""Compute current-flow betweenness centrality for edges. + + Current-flow betweenness centrality uses an electrical current + model for information spreading in contrast to betweenness + centrality which uses shortest paths. + + Current-flow betweenness centrality is also known as + random-walk betweenness centrality [2]_. + + Parameters + ---------- + G : graph + A NetworkX graph + + normalized : bool, optional (default=True) + If True the betweenness values are normalized by 2/[(n-1)(n-2)] where + n is the number of nodes in G. + + weight : string or None, optional (default=None) + Key for edge data used as the edge weight. + If None, then use 1 as each edge weight. + The weight reflects the capacity or the strength of the + edge. + + dtype : data type (default=float) + Default data type for internal matrices. + Set to np.float32 for lower memory consumption. + + solver : string (default='full') + Type of linear solver to use for computing the flow matrix. + Options are "full" (uses most memory), "lu" (recommended), and + "cg" (uses least memory). + + Returns + ------- + nodes : dictionary + Dictionary of edge tuples with betweenness centrality as the value. + + Raises + ------ + NetworkXError + The algorithm does not support DiGraphs. + If the input graph is an instance of DiGraph class, NetworkXError + is raised. + + See Also + -------- + betweenness_centrality + edge_betweenness_centrality + current_flow_betweenness_centrality + + Notes + ----- + Current-flow betweenness can be computed in $O(I(n-1)+mn \log n)$ + time [1]_, where $I(n-1)$ is the time needed to compute the + inverse Laplacian. For a full matrix this is $O(n^3)$ but using + sparse methods you can achieve $O(nm{\sqrt k})$ where $k$ is the + Laplacian matrix condition number. + + The space required is $O(nw)$ where $w$ is the width of the sparse + Laplacian matrix. Worse case is $w=n$ for $O(n^2)$. + + If the edges have a 'weight' attribute they will be used as + weights in this algorithm. Unspecified weights are set to 1. + + References + ---------- + .. [1] Centrality Measures Based on Current Flow. + Ulrik Brandes and Daniel Fleischer, + Proc. 22nd Symp. Theoretical Aspects of Computer Science (STACS '05). + LNCS 3404, pp. 533-544. Springer-Verlag, 2005. + https://doi.org/10.1007/978-3-540-31856-9_44 + + .. [2] A measure of betweenness centrality based on random walks, + M. E. J. Newman, Social Networks 27, 39-54 (2005). + """ + if not nx.is_connected(G): + raise nx.NetworkXError("Graph not connected.") + N = G.number_of_nodes() + ordering = list(reverse_cuthill_mckee_ordering(G)) + # make a copy with integer labels according to rcm ordering + # this could be done without a copy if we really wanted to + H = nx.relabel_nodes(G, dict(zip(ordering, range(N)))) + edges = (tuple(sorted((u, v))) for u, v in H.edges()) + betweenness = dict.fromkeys(edges, 0.0) + if normalized: + nb = (N - 1.0) * (N - 2.0) # normalization factor + else: + nb = 2.0 + for row, (e) in flow_matrix_row(H, weight=weight, dtype=dtype, solver=solver): + pos = dict(zip(row.argsort()[::-1], range(1, N + 1))) + for i in range(N): + betweenness[e] += (i + 1 - pos[i]) * row.item(i) + betweenness[e] += (N - i - pos[i]) * row.item(i) + betweenness[e] /= nb + return {(ordering[s], ordering[t]): b for (s, t), b in betweenness.items()} |