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< qpq`|S )a—  Returns communicability between all pairs of nodes in G.

    The communicability between pairs of nodes in G is the sum of
    walks of different lengths starting at node u and ending at node v.

    Parameters
    ----------
    G: graph

    Returns
    -------
    comm: dictionary of dictionaries
        Dictionary of dictionaries keyed by nodes with communicability
        as the value.

    Raises
    ------
    NetworkXError
       If the graph is not undirected and simple.

    See Also
    --------
    communicability_exp:
       Communicability between all pairs of nodes in G  using spectral
       decomposition.
    communicability_betweenness_centrality:
       Communicability betweenness centrality for each node in G.

    Notes
    -----
    This algorithm uses a spectral decomposition of the adjacency matrix.
    Let G=(V,E) be a simple undirected graph.  Using the connection between
    the powers  of the adjacency matrix and the number of walks in the graph,
    the communicability  between nodes `u` and `v` based on the graph spectrum
    is [1]_

    .. math::
        C(u,v)=\sum_{j=1}^{n}\phi_{j}(u)\phi_{j}(v)e^{\lambda_{j}},

    where `\phi_{j}(u)` is the `u\rm{th}` element of the `j\rm{th}` orthonormal
    eigenvector of the adjacency matrix associated with the eigenvalue
    `\lambda_{j}`.

    References
    ----------
    .. [1] Ernesto Estrada, Naomichi Hatano,
       "Communicability in complex networks",
       Phys. Rev. E 77, 036111 (2008).
       https://arxiv.org/abs/0707.0756

    Examples
    --------
    >>> G = nx.Graph([(0, 1), (1, 2), (1, 5), (5, 4), (2, 4), (2, 3), (4, 3), (3, 6)])
    >>> c = nx.communicability(G)
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    Communicability between pair of node (u,v) of node in G is the sum of
    walks of different lengths starting at node u and ending at node v.

    Parameters
    ----------
    G: graph

    Returns
    -------
    comm: dictionary of dictionaries
        Dictionary of dictionaries keyed by nodes with communicability
        as the value.

    Raises
    ------
    NetworkXError
        If the graph is not undirected and simple.

    See Also
    --------
    communicability:
       Communicability between pairs of nodes in G.
    communicability_betweenness_centrality:
       Communicability betweenness centrality for each node in G.

    Notes
    -----
    This algorithm uses matrix exponentiation of the adjacency matrix.

    Let G=(V,E) be a simple undirected graph.  Using the connection between
    the powers  of the adjacency matrix and the number of walks in the graph,
    the communicability between nodes u and v is [1]_,

    .. math::
        C(u,v) = (e^A)_{uv},

    where `A` is the adjacency matrix of G.

    References
    ----------
    .. [1] Ernesto Estrada, Naomichi Hatano,
       "Communicability in complex networks",
       Phys. Rev. E 77, 036111 (2008).
       https://arxiv.org/abs/0707.0756

    Examples
    --------
    >>> G = nx.Graph([(0, 1), (1, 2), (1, 5), (5, 4), (2, 4), (2, 3), (4, 3), (3, 6)])
    >>> c = nx.communicability_exp(G)
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