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diff --git a/.venv/lib/python3.12/site-packages/networkx/linalg/laplacianmatrix.py b/.venv/lib/python3.12/site-packages/networkx/linalg/laplacianmatrix.py new file mode 100644 index 00000000..d49ae491 --- /dev/null +++ b/.venv/lib/python3.12/site-packages/networkx/linalg/laplacianmatrix.py @@ -0,0 +1,617 @@ +"""Laplacian matrix of graphs. + +All calculations here are done using the out-degree. For Laplacians using +in-degree, use `G.reverse(copy=False)` instead of `G` and take the transpose. + +The `laplacian_matrix` function provides an unnormalized matrix, +while `normalized_laplacian_matrix`, `directed_laplacian_matrix`, +and `directed_combinatorial_laplacian_matrix` are all normalized. +""" + +import networkx as nx +from networkx.utils import not_implemented_for + +__all__ = [ + "laplacian_matrix", + "normalized_laplacian_matrix", + "total_spanning_tree_weight", + "directed_laplacian_matrix", + "directed_combinatorial_laplacian_matrix", +] + + +@nx._dispatchable(edge_attrs="weight") +def laplacian_matrix(G, nodelist=None, weight="weight"): + """Returns the Laplacian matrix of G. + + The graph Laplacian is the matrix L = D - A, where + A is the adjacency matrix and D is the diagonal matrix of node degrees. + + Parameters + ---------- + G : graph + A NetworkX graph + + nodelist : list, optional + The rows and columns are ordered according to the nodes in nodelist. + If nodelist is None, then the ordering is produced by G.nodes(). + + weight : string or None, optional (default='weight') + The edge data key used to compute each value in the matrix. + If None, then each edge has weight 1. + + Returns + ------- + L : SciPy sparse array + The Laplacian matrix of G. + + Notes + ----- + For MultiGraph, the edges weights are summed. + + This returns an unnormalized matrix. For a normalized output, + use `normalized_laplacian_matrix`, `directed_laplacian_matrix`, + or `directed_combinatorial_laplacian_matrix`. + + This calculation uses the out-degree of the graph `G`. To use the + in-degree for calculations instead, use `G.reverse(copy=False)` and + take the transpose. + + See Also + -------- + :func:`~networkx.convert_matrix.to_numpy_array` + normalized_laplacian_matrix + directed_laplacian_matrix + directed_combinatorial_laplacian_matrix + :func:`~networkx.linalg.spectrum.laplacian_spectrum` + + Examples + -------- + For graphs with multiple connected components, L is permutation-similar + to a block diagonal matrix where each block is the respective Laplacian + matrix for each component. + + >>> G = nx.Graph([(1, 2), (2, 3), (4, 5)]) + >>> print(nx.laplacian_matrix(G).toarray()) + [[ 1 -1 0 0 0] + [-1 2 -1 0 0] + [ 0 -1 1 0 0] + [ 0 0 0 1 -1] + [ 0 0 0 -1 1]] + + >>> edges = [ + ... (1, 2), + ... (2, 1), + ... (2, 4), + ... (4, 3), + ... (3, 4), + ... ] + >>> DiG = nx.DiGraph(edges) + >>> print(nx.laplacian_matrix(DiG).toarray()) + [[ 1 -1 0 0] + [-1 2 -1 0] + [ 0 0 1 -1] + [ 0 0 -1 1]] + + Notice that node 4 is represented by the third column and row. This is because + by default the row/column order is the order of `G.nodes` (i.e. the node added + order -- in the edgelist, 4 first appears in (2, 4), before node 3 in edge (4, 3).) + To control the node order of the matrix, use the `nodelist` argument. + + >>> print(nx.laplacian_matrix(DiG, nodelist=[1, 2, 3, 4]).toarray()) + [[ 1 -1 0 0] + [-1 2 0 -1] + [ 0 0 1 -1] + [ 0 0 -1 1]] + + This calculation uses the out-degree of the graph `G`. To use the + in-degree for calculations instead, use `G.reverse(copy=False)` and + take the transpose. + + >>> print(nx.laplacian_matrix(DiG.reverse(copy=False)).toarray().T) + [[ 1 -1 0 0] + [-1 1 -1 0] + [ 0 0 2 -1] + [ 0 0 -1 1]] + + References + ---------- + .. [1] Langville, Amy N., and Carl D. Meyer. Google’s PageRank and Beyond: + The Science of Search Engine Rankings. Princeton University Press, 2006. + + """ + import scipy as sp + + if nodelist is None: + nodelist = list(G) + A = nx.to_scipy_sparse_array(G, nodelist=nodelist, weight=weight, format="csr") + n, m = A.shape + # TODO: rm csr_array wrapper when spdiags can produce arrays + D = sp.sparse.csr_array(sp.sparse.spdiags(A.sum(axis=1), 0, m, n, format="csr")) + return D - A + + +@nx._dispatchable(edge_attrs="weight") +def normalized_laplacian_matrix(G, nodelist=None, weight="weight"): + r"""Returns the normalized Laplacian matrix of G. + + The normalized graph Laplacian is the matrix + + .. math:: + + N = D^{-1/2} L D^{-1/2} + + where `L` is the graph Laplacian and `D` is the diagonal matrix of + node degrees [1]_. + + Parameters + ---------- + G : graph + A NetworkX graph + + nodelist : list, optional + The rows and columns are ordered according to the nodes in nodelist. + If nodelist is None, then the ordering is produced by G.nodes(). + + weight : string or None, optional (default='weight') + The edge data key used to compute each value in the matrix. + If None, then each edge has weight 1. + + Returns + ------- + N : SciPy sparse array + The normalized Laplacian matrix of G. + + Notes + ----- + For MultiGraph, the edges weights are summed. + See :func:`to_numpy_array` for other options. + + If the Graph contains selfloops, D is defined as ``diag(sum(A, 1))``, where A is + the adjacency matrix [2]_. + + This calculation uses the out-degree of the graph `G`. To use the + in-degree for calculations instead, use `G.reverse(copy=False)` and + take the transpose. + + For an unnormalized output, use `laplacian_matrix`. + + Examples + -------- + + >>> import numpy as np + >>> edges = [ + ... (1, 2), + ... (2, 1), + ... (2, 4), + ... (4, 3), + ... (3, 4), + ... ] + >>> DiG = nx.DiGraph(edges) + >>> print(nx.normalized_laplacian_matrix(DiG).toarray()) + [[ 1. -0.70710678 0. 0. ] + [-0.70710678 1. -0.70710678 0. ] + [ 0. 0. 1. -1. ] + [ 0. 0. -1. 1. ]] + + Notice that node 4 is represented by the third column and row. This is because + by default the row/column order is the order of `G.nodes` (i.e. the node added + order -- in the edgelist, 4 first appears in (2, 4), before node 3 in edge (4, 3).) + To control the node order of the matrix, use the `nodelist` argument. + + >>> print(nx.normalized_laplacian_matrix(DiG, nodelist=[1, 2, 3, 4]).toarray()) + [[ 1. -0.70710678 0. 0. ] + [-0.70710678 1. 0. -0.70710678] + [ 0. 0. 1. -1. ] + [ 0. 0. -1. 1. ]] + >>> G = nx.Graph(edges) + >>> print(nx.normalized_laplacian_matrix(G).toarray()) + [[ 1. -0.70710678 0. 0. ] + [-0.70710678 1. -0.5 0. ] + [ 0. -0.5 1. -0.70710678] + [ 0. 0. -0.70710678 1. ]] + + See Also + -------- + laplacian_matrix + normalized_laplacian_spectrum + directed_laplacian_matrix + directed_combinatorial_laplacian_matrix + + References + ---------- + .. [1] Fan Chung-Graham, Spectral Graph Theory, + CBMS Regional Conference Series in Mathematics, Number 92, 1997. + .. [2] Steve Butler, Interlacing For Weighted Graphs Using The Normalized + Laplacian, Electronic Journal of Linear Algebra, Volume 16, pp. 90-98, + March 2007. + .. [3] Langville, Amy N., and Carl D. Meyer. Google’s PageRank and Beyond: + The Science of Search Engine Rankings. Princeton University Press, 2006. + """ + import numpy as np + import scipy as sp + + if nodelist is None: + nodelist = list(G) + A = nx.to_scipy_sparse_array(G, nodelist=nodelist, weight=weight, format="csr") + n, _ = A.shape + diags = A.sum(axis=1) + # TODO: rm csr_array wrapper when spdiags can produce arrays + D = sp.sparse.csr_array(sp.sparse.spdiags(diags, 0, n, n, format="csr")) + L = D - A + with np.errstate(divide="ignore"): + diags_sqrt = 1.0 / np.sqrt(diags) + diags_sqrt[np.isinf(diags_sqrt)] = 0 + # TODO: rm csr_array wrapper when spdiags can produce arrays + DH = sp.sparse.csr_array(sp.sparse.spdiags(diags_sqrt, 0, n, n, format="csr")) + return DH @ (L @ DH) + + +@nx._dispatchable(edge_attrs="weight") +def total_spanning_tree_weight(G, weight=None, root=None): + """ + Returns the total weight of all spanning trees of `G`. + + Kirchoff's Tree Matrix Theorem [1]_, [2]_ states that the determinant of any + cofactor of the Laplacian matrix of a graph is the number of spanning trees + in the graph. For a weighted Laplacian matrix, it is the sum across all + spanning trees of the multiplicative weight of each tree. That is, the + weight of each tree is the product of its edge weights. + + For unweighted graphs, the total weight equals the number of spanning trees in `G`. + + For directed graphs, the total weight follows by summing over all directed + spanning trees in `G` that start in the `root` node [3]_. + + .. deprecated:: 3.3 + + ``total_spanning_tree_weight`` is deprecated and will be removed in v3.5. + Use ``nx.number_of_spanning_trees(G)`` instead. + + Parameters + ---------- + G : NetworkX Graph + + weight : string or None, optional (default=None) + The key for the edge attribute holding the edge weight. + If None, then each edge has weight 1. + + root : node (only required for directed graphs) + A node in the directed graph `G`. + + Returns + ------- + total_weight : float + Undirected graphs: + The sum of the total multiplicative weights for all spanning trees in `G`. + Directed graphs: + The sum of the total multiplicative weights for all spanning trees of `G`, + rooted at node `root`. + + Raises + ------ + NetworkXPointlessConcept + If `G` does not contain any nodes. + + NetworkXError + If the graph `G` is not (weakly) connected, + or if `G` is directed and the root node is not specified or not in G. + + Examples + -------- + >>> G = nx.complete_graph(5) + >>> round(nx.total_spanning_tree_weight(G)) + 125 + + >>> G = nx.Graph() + >>> G.add_edge(1, 2, weight=2) + >>> G.add_edge(1, 3, weight=1) + >>> G.add_edge(2, 3, weight=1) + >>> round(nx.total_spanning_tree_weight(G, "weight")) + 5 + + Notes + ----- + Self-loops are excluded. Multi-edges are contracted in one edge + equal to the sum of the weights. + + References + ---------- + .. [1] Wikipedia + "Kirchhoff's theorem." + https://en.wikipedia.org/wiki/Kirchhoff%27s_theorem + .. [2] Kirchhoff, G. R. + Über die Auflösung der Gleichungen, auf welche man + bei der Untersuchung der linearen Vertheilung + Galvanischer Ströme geführt wird + Annalen der Physik und Chemie, vol. 72, pp. 497-508, 1847. + .. [3] Margoliash, J. + "Matrix-Tree Theorem for Directed Graphs" + https://www.math.uchicago.edu/~may/VIGRE/VIGRE2010/REUPapers/Margoliash.pdf + """ + import warnings + + warnings.warn( + ( + "\n\ntotal_spanning_tree_weight is deprecated and will be removed in v3.5.\n" + "Use `nx.number_of_spanning_trees(G)` instead." + ), + category=DeprecationWarning, + stacklevel=3, + ) + + return nx.number_of_spanning_trees(G, weight=weight, root=root) + + +############################################################################### +# Code based on work from https://github.com/bjedwards + + +@not_implemented_for("undirected") +@not_implemented_for("multigraph") +@nx._dispatchable(edge_attrs="weight") +def directed_laplacian_matrix( + G, nodelist=None, weight="weight", walk_type=None, alpha=0.95 +): + r"""Returns the directed Laplacian matrix of G. + + The graph directed Laplacian is the matrix + + .. math:: + + L = I - \frac{1}{2} \left (\Phi^{1/2} P \Phi^{-1/2} + \Phi^{-1/2} P^T \Phi^{1/2} \right ) + + where `I` is the identity matrix, `P` is the transition matrix of the + graph, and `\Phi` a matrix with the Perron vector of `P` in the diagonal and + zeros elsewhere [1]_. + + Depending on the value of walk_type, `P` can be the transition matrix + induced by a random walk, a lazy random walk, or a random walk with + teleportation (PageRank). + + Parameters + ---------- + G : DiGraph + A NetworkX graph + + nodelist : list, optional + The rows and columns are ordered according to the nodes in nodelist. + If nodelist is None, then the ordering is produced by G.nodes(). + + weight : string or None, optional (default='weight') + The edge data key used to compute each value in the matrix. + If None, then each edge has weight 1. + + walk_type : string or None, optional (default=None) + One of ``"random"``, ``"lazy"``, or ``"pagerank"``. If ``walk_type=None`` + (the default), then a value is selected according to the properties of `G`: + - ``walk_type="random"`` if `G` is strongly connected and aperiodic + - ``walk_type="lazy"`` if `G` is strongly connected but not aperiodic + - ``walk_type="pagerank"`` for all other cases. + + alpha : real + (1 - alpha) is the teleportation probability used with pagerank + + Returns + ------- + L : NumPy matrix + Normalized Laplacian of G. + + Notes + ----- + Only implemented for DiGraphs + + The result is always a symmetric matrix. + + This calculation uses the out-degree of the graph `G`. To use the + in-degree for calculations instead, use `G.reverse(copy=False)` and + take the transpose. + + See Also + -------- + laplacian_matrix + normalized_laplacian_matrix + directed_combinatorial_laplacian_matrix + + References + ---------- + .. [1] Fan Chung (2005). + Laplacians and the Cheeger inequality for directed graphs. + Annals of Combinatorics, 9(1), 2005 + """ + import numpy as np + import scipy as sp + + # NOTE: P has type ndarray if walk_type=="pagerank", else csr_array + P = _transition_matrix( + G, nodelist=nodelist, weight=weight, walk_type=walk_type, alpha=alpha + ) + + n, m = P.shape + + evals, evecs = sp.sparse.linalg.eigs(P.T, k=1) + v = evecs.flatten().real + p = v / v.sum() + # p>=0 by Perron-Frobenius Thm. Use abs() to fix roundoff across zero gh-6865 + sqrtp = np.sqrt(np.abs(p)) + Q = ( + # TODO: rm csr_array wrapper when spdiags creates arrays + sp.sparse.csr_array(sp.sparse.spdiags(sqrtp, 0, n, n)) + @ P + # TODO: rm csr_array wrapper when spdiags creates arrays + @ sp.sparse.csr_array(sp.sparse.spdiags(1.0 / sqrtp, 0, n, n)) + ) + # NOTE: This could be sparsified for the non-pagerank cases + I = np.identity(len(G)) + + return I - (Q + Q.T) / 2.0 + + +@not_implemented_for("undirected") +@not_implemented_for("multigraph") +@nx._dispatchable(edge_attrs="weight") +def directed_combinatorial_laplacian_matrix( + G, nodelist=None, weight="weight", walk_type=None, alpha=0.95 +): + r"""Return the directed combinatorial Laplacian matrix of G. + + The graph directed combinatorial Laplacian is the matrix + + .. math:: + + L = \Phi - \frac{1}{2} \left (\Phi P + P^T \Phi \right) + + where `P` is the transition matrix of the graph and `\Phi` a matrix + with the Perron vector of `P` in the diagonal and zeros elsewhere [1]_. + + Depending on the value of walk_type, `P` can be the transition matrix + induced by a random walk, a lazy random walk, or a random walk with + teleportation (PageRank). + + Parameters + ---------- + G : DiGraph + A NetworkX graph + + nodelist : list, optional + The rows and columns are ordered according to the nodes in nodelist. + If nodelist is None, then the ordering is produced by G.nodes(). + + weight : string or None, optional (default='weight') + The edge data key used to compute each value in the matrix. + If None, then each edge has weight 1. + + walk_type : string or None, optional (default=None) + One of ``"random"``, ``"lazy"``, or ``"pagerank"``. If ``walk_type=None`` + (the default), then a value is selected according to the properties of `G`: + - ``walk_type="random"`` if `G` is strongly connected and aperiodic + - ``walk_type="lazy"`` if `G` is strongly connected but not aperiodic + - ``walk_type="pagerank"`` for all other cases. + + alpha : real + (1 - alpha) is the teleportation probability used with pagerank + + Returns + ------- + L : NumPy matrix + Combinatorial Laplacian of G. + + Notes + ----- + Only implemented for DiGraphs + + The result is always a symmetric matrix. + + This calculation uses the out-degree of the graph `G`. To use the + in-degree for calculations instead, use `G.reverse(copy=False)` and + take the transpose. + + See Also + -------- + laplacian_matrix + normalized_laplacian_matrix + directed_laplacian_matrix + + References + ---------- + .. [1] Fan Chung (2005). + Laplacians and the Cheeger inequality for directed graphs. + Annals of Combinatorics, 9(1), 2005 + """ + import scipy as sp + + P = _transition_matrix( + G, nodelist=nodelist, weight=weight, walk_type=walk_type, alpha=alpha + ) + + n, m = P.shape + + evals, evecs = sp.sparse.linalg.eigs(P.T, k=1) + v = evecs.flatten().real + p = v / v.sum() + # NOTE: could be improved by not densifying + # TODO: Rm csr_array wrapper when spdiags array creation becomes available + Phi = sp.sparse.csr_array(sp.sparse.spdiags(p, 0, n, n)).toarray() + + return Phi - (Phi @ P + P.T @ Phi) / 2.0 + + +def _transition_matrix(G, nodelist=None, weight="weight", walk_type=None, alpha=0.95): + """Returns the transition matrix of G. + + This is a row stochastic giving the transition probabilities while + performing a random walk on the graph. Depending on the value of walk_type, + P can be the transition matrix induced by a random walk, a lazy random walk, + or a random walk with teleportation (PageRank). + + Parameters + ---------- + G : DiGraph + A NetworkX graph + + nodelist : list, optional + The rows and columns are ordered according to the nodes in nodelist. + If nodelist is None, then the ordering is produced by G.nodes(). + + weight : string or None, optional (default='weight') + The edge data key used to compute each value in the matrix. + If None, then each edge has weight 1. + + walk_type : string or None, optional (default=None) + One of ``"random"``, ``"lazy"``, or ``"pagerank"``. If ``walk_type=None`` + (the default), then a value is selected according to the properties of `G`: + - ``walk_type="random"`` if `G` is strongly connected and aperiodic + - ``walk_type="lazy"`` if `G` is strongly connected but not aperiodic + - ``walk_type="pagerank"`` for all other cases. + + alpha : real + (1 - alpha) is the teleportation probability used with pagerank + + Returns + ------- + P : numpy.ndarray + transition matrix of G. + + Raises + ------ + NetworkXError + If walk_type not specified or alpha not in valid range + """ + import numpy as np + import scipy as sp + + if walk_type is None: + if nx.is_strongly_connected(G): + if nx.is_aperiodic(G): + walk_type = "random" + else: + walk_type = "lazy" + else: + walk_type = "pagerank" + + A = nx.to_scipy_sparse_array(G, nodelist=nodelist, weight=weight, dtype=float) + n, m = A.shape + if walk_type in ["random", "lazy"]: + # TODO: Rm csr_array wrapper when spdiags array creation becomes available + DI = sp.sparse.csr_array(sp.sparse.spdiags(1.0 / A.sum(axis=1), 0, n, n)) + if walk_type == "random": + P = DI @ A + else: + # TODO: Rm csr_array wrapper when identity array creation becomes available + I = sp.sparse.csr_array(sp.sparse.identity(n)) + P = (I + DI @ A) / 2.0 + + elif walk_type == "pagerank": + if not (0 < alpha < 1): + raise nx.NetworkXError("alpha must be between 0 and 1") + # this is using a dense representation. NOTE: This should be sparsified! + A = A.toarray() + # add constant to dangling nodes' row + A[A.sum(axis=1) == 0, :] = 1 / n + # normalize + A = A / A.sum(axis=1)[np.newaxis, :].T + P = alpha * A + (1 - alpha) / n + else: + raise nx.NetworkXError("walk_type must be random, lazy, or pagerank") + + return P |