Fixed database typo and removed unnecessary class identifier.

venv/Lib/site-packages/networkx/algorithms/richclub.py

@@ -0,0 +1,119 @@
+"""Functions for computing rich-club coefficients."""
+
+import networkx as nx
+from itertools import accumulate
+from networkx.utils import not_implemented_for
+
+__all__ = ["rich_club_coefficient"]
+
+
+@not_implemented_for("directed")
+@not_implemented_for("multigraph")
+def rich_club_coefficient(G, normalized=True, Q=100, seed=None):
+    r"""Returns the rich-club coefficient of the graph `G`.
+
+    For each degree *k*, the *rich-club coefficient* is the ratio of the
+    number of actual to the number of potential edges for nodes with
+    degree greater than *k*:
+
+    .. math::
+
+        \phi(k) = \frac{2 E_k}{N_k (N_k - 1)}
+
+    where `N_k` is the number of nodes with degree larger than *k*, and
+    `E_k` is the number of edges among those nodes.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        Undirected graph with neither parallel edges nor self-loops.
+    normalized : bool (optional)
+        Normalize using randomized network as in [1]_
+    Q : float (optional, default=100)
+        If `normalized` is True, perform `Q * m` double-edge
+        swaps, where `m` is the number of edges in `G`, to use as a
+        null-model for normalization.
+    seed : integer, random_state, or None (default)
+        Indicator of random number generation state.
+        See :ref:`Randomness<randomness>`.
+
+    Returns
+    -------
+    rc : dictionary
+       A dictionary, keyed by degree, with rich-club coefficient values.
+
+    Examples
+    --------
+    >>> G = nx.Graph([(0, 1), (0, 2), (1, 2), (1, 3), (1, 4), (4, 5)])
+    >>> rc = nx.rich_club_coefficient(G, normalized=False, seed=42)
+    >>> rc[0]
+    0.4
+
+    Notes
+    -----
+    The rich club definition and algorithm are found in [1]_.  This
+    algorithm ignores any edge weights and is not defined for directed
+    graphs or graphs with parallel edges or self loops.
+
+    Estimates for appropriate values of `Q` are found in [2]_.
+
+    References
+    ----------
+    .. [1] Julian J. McAuley, Luciano da Fontoura Costa,
+       and Tibério S. Caetano,
+       "The rich-club phenomenon across complex network hierarchies",
+       Applied Physics Letters Vol 91 Issue 8, August 2007.
+       https://arxiv.org/abs/physics/0701290
+    .. [2] R. Milo, N. Kashtan, S. Itzkovitz, M. E. J. Newman, U. Alon,
+       "Uniform generation of random graphs with arbitrary degree
+       sequences", 2006. https://arxiv.org/abs/cond-mat/0312028
+    """
+    if nx.number_of_selfloops(G) > 0:
+        raise Exception(
+            "rich_club_coefficient is not implemented for " "graphs with self loops."
+        )
+    rc = _compute_rc(G)
+    if normalized:
+        # make R a copy of G, randomize with Q*|E| double edge swaps
+        # and use rich_club coefficient of R to normalize
+        R = G.copy()
+        E = R.number_of_edges()
+        nx.double_edge_swap(R, Q * E, max_tries=Q * E * 10, seed=seed)
+        rcran = _compute_rc(R)
+        rc = {k: v / rcran[k] for k, v in rc.items()}
+    return rc
+
+
+def _compute_rc(G):
+    """Returns the rich-club coefficient for each degree in the graph
+    `G`.
+
+    `G` is an undirected graph without multiedges.
+
+    Returns a dictionary mapping degree to rich-club coefficient for
+    that degree.
+
+    """
+    deghist = nx.degree_histogram(G)
+    total = sum(deghist)
+    # Compute the number of nodes with degree greater than `k`, for each
+    # degree `k` (omitting the last entry, which is zero).
+    nks = (total - cs for cs in accumulate(deghist) if total - cs > 1)
+    # Create a sorted list of pairs of edge endpoint degrees.
+    #
+    # The list is sorted in reverse order so that we can pop from the
+    # right side of the list later, instead of popping from the left
+    # side of the list, which would have a linear time cost.
+    edge_degrees = sorted((sorted(map(G.degree, e)) for e in G.edges()), reverse=True)
+    ek = G.number_of_edges()
+    k1, k2 = edge_degrees.pop()
+    rc = {}
+    for d, nk in enumerate(nks):
+        while k1 <= d:
+            if len(edge_degrees) == 0:
+                ek = 0
+                break
+            k1, k2 = edge_degrees.pop()
+            ek -= 1
+        rc[d] = 2 * ek / (nk * (nk - 1))
+    return rc