| """ |
| Eigenvalue spectrum of graphs. |
| """ |
| # Copyright (C) 2004-2011 by |
| # Aric Hagberg <hagberg@lanl.gov> |
| # Dan Schult <dschult@colgate.edu> |
| # Pieter Swart <swart@lanl.gov> |
| # All rights reserved. |
| # BSD license. |
| import networkx as nx |
| __author__ = "\n".join(['Aric Hagberg (hagberg@lanl.gov)', |
| 'Pieter Swart (swart@lanl.gov)', |
| 'Dan Schult(dschult@colgate.edu)']) |
| |
| __all__ = ['laplacian_spectrum', 'adjacency_spectrum'] |
| |
| |
| def laplacian_spectrum(G, weight='weight'): |
| """Return 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 to_numpy_matrix for other options. |
| |
| See Also |
| -------- |
| laplacian_matrix |
| """ |
| try: |
| import numpy as np |
| except ImportError: |
| raise ImportError( |
| "laplacian_spectrum() requires NumPy: http://scipy.org/ ") |
| return np.linalg.eigvals(nx.laplacian_matrix(G,weight=weight)) |
| |
| def adjacency_spectrum(G, weight='weight'): |
| """Return 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_matrix for other options. |
| |
| See Also |
| -------- |
| adjacency_matrix |
| """ |
| try: |
| import numpy as np |
| except ImportError: |
| raise ImportError( |
| "adjacency_spectrum() requires NumPy: http://scipy.org/ ") |
| return np.linalg.eigvals(nx.adjacency_matrix(G,weight=weight)) |
| |
| # fixture for nose tests |
| def setup_module(module): |
| from nose import SkipTest |
| try: |
| import numpy |
| except: |
| raise SkipTest("NumPy not available") |
