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authorS. Solomon Darnell2025-03-28 21:52:21 -0500
committerS. Solomon Darnell2025-03-28 21:52:21 -0500
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treeee3dc5af3b6313e921cd920906356f5d4febc4ed /.venv/lib/python3.12/site-packages/networkx/linalg/spectrum.py
parentcc961e04ba734dd72309fb548a2f97d67d578813 (diff)
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+"""
+Eigenvalue spectrum of graphs.
+"""
+
+import networkx as nx
+
+__all__ = [
+ "laplacian_spectrum",
+ "adjacency_spectrum",
+ "modularity_spectrum",
+ "normalized_laplacian_spectrum",
+ "bethe_hessian_spectrum",
+]
+
+
+@nx._dispatchable(edge_attrs="weight")
+def laplacian_spectrum(G, weight="weight"):
+ """Returns eigenvalues of the Laplacian of G
+
+ Parameters
+ ----------
+ G : graph
+ A NetworkX graph
+
+ 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
+ -------
+ evals : NumPy array
+ Eigenvalues
+
+ Notes
+ -----
+ For MultiGraph/MultiDiGraph, the edges weights are summed.
+ See :func:`~networkx.convert_matrix.to_numpy_array` for other options.
+
+ See Also
+ --------
+ laplacian_matrix
+
+ Examples
+ --------
+ The multiplicity of 0 as an eigenvalue of the laplacian matrix is equal
+ to the number of connected components of G.
+
+ >>> G = nx.Graph() # Create a graph with 5 nodes and 3 connected components
+ >>> G.add_nodes_from(range(5))
+ >>> G.add_edges_from([(0, 2), (3, 4)])
+ >>> nx.laplacian_spectrum(G)
+ array([0., 0., 0., 2., 2.])
+
+ """
+ import scipy as sp
+
+ return sp.linalg.eigvalsh(nx.laplacian_matrix(G, weight=weight).todense())
+
+
+@nx._dispatchable(edge_attrs="weight")
+def normalized_laplacian_spectrum(G, weight="weight"):
+ """Return eigenvalues of the normalized Laplacian of G
+
+ Parameters
+ ----------
+ G : graph
+ A NetworkX graph
+
+ 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
+ -------
+ evals : NumPy array
+ Eigenvalues
+
+ Notes
+ -----
+ For MultiGraph/MultiDiGraph, the edges weights are summed.
+ See to_numpy_array for other options.
+
+ See Also
+ --------
+ normalized_laplacian_matrix
+ """
+ import scipy as sp
+
+ return sp.linalg.eigvalsh(
+ nx.normalized_laplacian_matrix(G, weight=weight).todense()
+ )
+
+
+@nx._dispatchable(edge_attrs="weight")
+def adjacency_spectrum(G, weight="weight"):
+ """Returns eigenvalues of the adjacency matrix of G.
+
+ Parameters
+ ----------
+ G : graph
+ A NetworkX graph
+
+ 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
+ -------
+ evals : NumPy array
+ Eigenvalues
+
+ Notes
+ -----
+ For MultiGraph/MultiDiGraph, the edges weights are summed.
+ See to_numpy_array for other options.
+
+ See Also
+ --------
+ adjacency_matrix
+ """
+ import scipy as sp
+
+ return sp.linalg.eigvals(nx.adjacency_matrix(G, weight=weight).todense())
+
+
+@nx._dispatchable
+def modularity_spectrum(G):
+ """Returns eigenvalues of the modularity matrix of G.
+
+ Parameters
+ ----------
+ G : Graph
+ A NetworkX Graph or DiGraph
+
+ Returns
+ -------
+ evals : NumPy array
+ Eigenvalues
+
+ See Also
+ --------
+ modularity_matrix
+
+ References
+ ----------
+ .. [1] M. E. J. Newman, "Modularity and community structure in networks",
+ Proc. Natl. Acad. Sci. USA, vol. 103, pp. 8577-8582, 2006.
+ """
+ import scipy as sp
+
+ if G.is_directed():
+ return sp.linalg.eigvals(nx.directed_modularity_matrix(G))
+ else:
+ return sp.linalg.eigvals(nx.modularity_matrix(G))
+
+
+@nx._dispatchable
+def bethe_hessian_spectrum(G, r=None):
+ """Returns eigenvalues of the Bethe Hessian matrix of G.
+
+ Parameters
+ ----------
+ G : Graph
+ A NetworkX Graph or DiGraph
+
+ r : float
+ Regularizer parameter
+
+ Returns
+ -------
+ evals : NumPy array
+ Eigenvalues
+
+ See Also
+ --------
+ bethe_hessian_matrix
+
+ References
+ ----------
+ .. [1] A. Saade, F. Krzakala and L. Zdeborová
+ "Spectral clustering of graphs with the bethe hessian",
+ Advances in Neural Information Processing Systems. 2014.
+ """
+ import scipy as sp
+
+ return sp.linalg.eigvalsh(nx.bethe_hessian_matrix(G, r).todense())