spectral_ordering

spectral_ordering(G, weight='weight', normalized=False, tol=1e-08, method='tracemin')

Compute the spectral_ordering of a graph.

The spectral ordering of a graph is an ordering of its nodes where nodes in the same weakly connected components appear contiguous and ordered by their corresponding elements in the Fiedler vector of the component.

Parameters:

G : NetworkX graph

A graph.

weight : object, optional

The data key used to determine the weight of each edge. If None, then each edge has unit weight. Default value: None.

normalized : bool, optional

Whether the normalized Laplacian matrix is used. Default value: False.

tol : float, optional

Tolerance of relative residual in eigenvalue computation. Default value: 1e-8.

method : string, optional

Method of eigenvalue computation. It should be one of ‘tracemin’ (TraceMIN), ‘lanczos’ (Lanczos iteration) and ‘lobpcg’ (LOBPCG). Default value: ‘tracemin’.

The TraceMIN algorithm uses a linear system solver. The following values allow specifying the solver to be used.

Value	Solver
‘tracemin_pcg’	Preconditioned conjugate gradient method
‘tracemin_chol’	Cholesky factorization
‘tracemin_lu’	LU factorization

Returns:

spectral_ordering : NumPy array of floats.

Spectral ordering of nodes.

Raises:

NetworkXError :

If G is empty.

See also

laplacian_matrix

Notes

Edge weights are interpreted by their absolute values. For MultiGraph’s, weights of parallel edges are summed. Zero-weighted edges are ignored.

To use Cholesky factorization in the TraceMIN algorithm, the scikits.sparse package must be installed.