networkx.algorithms.centrality.estrada_index¶
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estrada_index
(G)[source]¶ Return the Estrada index of a the graph G.
The Estrada Index is a topological index of folding or 3D “compactness” ([1]).
Parameters: G (graph) Returns: estrada index Return type: float Raises: NetworkXError
– If the graph is not undirected and simple.Notes
Let
G=(V,E)
be a simple undirected graph withn
nodes and letlambda_{1}leqlambda_{2}leqcdotslambda_{n}
be a non-increasing ordering of the eigenvalues of its adjacency matrixA
. The Estrada index is ([1], [2])\[EE(G)=\sum_{j=1}^n e^{\lambda _j}.\]References
[1] (1, 2) E. Estrada, “Characterization of 3D molecular structure”, Chem. Phys. Lett. 319, 713 (2000). http://dx.doi.org/10.1016/S0009-2614(00)00158-5 [2] José Antonio de la Peñaa, Ivan Gutman, Juan Rada, “Estimating the Estrada index”, Linear Algebra and its Applications. 427, 1 (2007). http://dx.doi.org/10.1016/j.laa.2007.06.020 Examples
>>> G=nx.Graph([(0,1),(1,2),(1,5),(5,4),(2,4),(2,3),(4,3),(3,6)]) >>> ei=nx.estrada_index(G)