Mercurial > repos > shellac > sam_consensus_v3
diff env/lib/python3.9/site-packages/networkx/generators/random_graphs.py @ 0:4f3585e2f14b draft default tip
"planemo upload commit 60cee0fc7c0cda8592644e1aad72851dec82c959"
| author | shellac |
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| date | Mon, 22 Mar 2021 18:12:50 +0000 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/env/lib/python3.9/site-packages/networkx/generators/random_graphs.py Mon Mar 22 18:12:50 2021 +0000 @@ -0,0 +1,1295 @@ +""" +Generators for random graphs. + +""" + +import itertools +import math + +import networkx as nx +from networkx.utils import py_random_state +from .classic import empty_graph, path_graph, complete_graph +from .degree_seq import degree_sequence_tree +from collections import defaultdict + +__all__ = [ + "fast_gnp_random_graph", + "gnp_random_graph", + "dense_gnm_random_graph", + "gnm_random_graph", + "erdos_renyi_graph", + "binomial_graph", + "newman_watts_strogatz_graph", + "watts_strogatz_graph", + "connected_watts_strogatz_graph", + "random_regular_graph", + "barabasi_albert_graph", + "dual_barabasi_albert_graph", + "extended_barabasi_albert_graph", + "powerlaw_cluster_graph", + "random_lobster", + "random_shell_graph", + "random_powerlaw_tree", + "random_powerlaw_tree_sequence", + "random_kernel_graph", +] + + +@py_random_state(2) +def fast_gnp_random_graph(n, p, seed=None, directed=False): + """Returns a $G_{n,p}$ random graph, also known as an Erdős-Rényi graph or + a binomial graph. + + Parameters + ---------- + n : int + The number of nodes. + p : float + Probability for edge creation. + seed : integer, random_state, or None (default) + Indicator of random number generation state. + See :ref:`Randomness<randomness>`. + directed : bool, optional (default=False) + If True, this function returns a directed graph. + + Notes + ----- + The $G_{n,p}$ graph algorithm chooses each of the $[n (n - 1)] / 2$ + (undirected) or $n (n - 1)$ (directed) possible edges with probability $p$. + + This algorithm [1]_ runs in $O(n + m)$ time, where `m` is the expected number of + edges, which equals $p n (n - 1) / 2$. This should be faster than + :func:`gnp_random_graph` when $p$ is small and the expected number of edges + is small (that is, the graph is sparse). + + See Also + -------- + gnp_random_graph + + References + ---------- + .. [1] Vladimir Batagelj and Ulrik Brandes, + "Efficient generation of large random networks", + Phys. Rev. E, 71, 036113, 2005. + """ + G = empty_graph(n) + + if p <= 0 or p >= 1: + return nx.gnp_random_graph(n, p, seed=seed, directed=directed) + + w = -1 + lp = math.log(1.0 - p) + + if directed: + G = nx.DiGraph(G) + # Nodes in graph are from 0,n-1 (start with v as the first node index). + v = 0 + while v < n: + lr = math.log(1.0 - seed.random()) + w = w + 1 + int(lr / lp) + if v == w: # avoid self loops + w = w + 1 + while v < n <= w: + w = w - n + v = v + 1 + if v == w: # avoid self loops + w = w + 1 + if v < n: + G.add_edge(v, w) + else: + # Nodes in graph are from 0,n-1 (start with v as the second node index). + v = 1 + while v < n: + lr = math.log(1.0 - seed.random()) + w = w + 1 + int(lr / lp) + while w >= v and v < n: + w = w - v + v = v + 1 + if v < n: + G.add_edge(v, w) + return G + + +@py_random_state(2) +def gnp_random_graph(n, p, seed=None, directed=False): + """Returns a $G_{n,p}$ random graph, also known as an Erdős-Rényi graph + or a binomial graph. + + The $G_{n,p}$ model chooses each of the possible edges with probability $p$. + + Parameters + ---------- + n : int + The number of nodes. + p : float + Probability for edge creation. + seed : integer, random_state, or None (default) + Indicator of random number generation state. + See :ref:`Randomness<randomness>`. + directed : bool, optional (default=False) + If True, this function returns a directed graph. + + See Also + -------- + fast_gnp_random_graph + + Notes + ----- + This algorithm [2]_ runs in $O(n^2)$ time. For sparse graphs (that is, for + small values of $p$), :func:`fast_gnp_random_graph` is a faster algorithm. + + :func:`binomial_graph` and :func:`erdos_renyi_graph` are + aliases for :func:`gnp_random_graph`. + + >>> nx.binomial_graph is nx.gnp_random_graph + True + >>> nx.erdos_renyi_graph is nx.gnp_random_graph + True + + References + ---------- + .. [1] P. Erdős and A. Rényi, On Random Graphs, Publ. Math. 6, 290 (1959). + .. [2] E. N. Gilbert, Random Graphs, Ann. Math. Stat., 30, 1141 (1959). + """ + if directed: + edges = itertools.permutations(range(n), 2) + G = nx.DiGraph() + else: + edges = itertools.combinations(range(n), 2) + G = nx.Graph() + G.add_nodes_from(range(n)) + if p <= 0: + return G + if p >= 1: + return complete_graph(n, create_using=G) + + for e in edges: + if seed.random() < p: + G.add_edge(*e) + return G + + +# add some aliases to common names +binomial_graph = gnp_random_graph +erdos_renyi_graph = gnp_random_graph + + +@py_random_state(2) +def dense_gnm_random_graph(n, m, seed=None): + """Returns a $G_{n,m}$ random graph. + + In the $G_{n,m}$ model, a graph is chosen uniformly at random from the set + of all graphs with $n$ nodes and $m$ edges. + + This algorithm should be faster than :func:`gnm_random_graph` for dense + graphs. + + Parameters + ---------- + n : int + The number of nodes. + m : int + The number of edges. + seed : integer, random_state, or None (default) + Indicator of random number generation state. + See :ref:`Randomness<randomness>`. + + See Also + -------- + gnm_random_graph() + + Notes + ----- + Algorithm by Keith M. Briggs Mar 31, 2006. + Inspired by Knuth's Algorithm S (Selection sampling technique), + in section 3.4.2 of [1]_. + + References + ---------- + .. [1] Donald E. Knuth, The Art of Computer Programming, + Volume 2/Seminumerical algorithms, Third Edition, Addison-Wesley, 1997. + """ + mmax = n * (n - 1) / 2 + if m >= mmax: + G = complete_graph(n) + else: + G = empty_graph(n) + + if n == 1 or m >= mmax: + return G + + u = 0 + v = 1 + t = 0 + k = 0 + while True: + if seed.randrange(mmax - t) < m - k: + G.add_edge(u, v) + k += 1 + if k == m: + return G + t += 1 + v += 1 + if v == n: # go to next row of adjacency matrix + u += 1 + v = u + 1 + + +@py_random_state(2) +def gnm_random_graph(n, m, seed=None, directed=False): + """Returns a $G_{n,m}$ random graph. + + In the $G_{n,m}$ model, a graph is chosen uniformly at random from the set + of all graphs with $n$ nodes and $m$ edges. + + This algorithm should be faster than :func:`dense_gnm_random_graph` for + sparse graphs. + + Parameters + ---------- + n : int + The number of nodes. + m : int + The number of edges. + seed : integer, random_state, or None (default) + Indicator of random number generation state. + See :ref:`Randomness<randomness>`. + directed : bool, optional (default=False) + If True return a directed graph + + See also + -------- + dense_gnm_random_graph + + """ + if directed: + G = nx.DiGraph() + else: + G = nx.Graph() + G.add_nodes_from(range(n)) + + if n == 1: + return G + max_edges = n * (n - 1) + if not directed: + max_edges /= 2.0 + if m >= max_edges: + return complete_graph(n, create_using=G) + + nlist = list(G) + edge_count = 0 + while edge_count < m: + # generate random edge,u,v + u = seed.choice(nlist) + v = seed.choice(nlist) + if u == v or G.has_edge(u, v): + continue + else: + G.add_edge(u, v) + edge_count = edge_count + 1 + return G + + +@py_random_state(3) +def newman_watts_strogatz_graph(n, k, p, seed=None): + """Returns a Newman–Watts–Strogatz small-world graph. + + Parameters + ---------- + n : int + The number of nodes. + k : int + Each node is joined with its `k` nearest neighbors in a ring + topology. + p : float + The probability of adding a new edge for each edge. + seed : integer, random_state, or None (default) + Indicator of random number generation state. + See :ref:`Randomness<randomness>`. + + Notes + ----- + First create a ring over $n$ nodes [1]_. Then each node in the ring is + connected with its $k$ nearest neighbors (or $k - 1$ neighbors if $k$ + is odd). Then shortcuts are created by adding new edges as follows: for + each edge $(u, v)$ in the underlying "$n$-ring with $k$ nearest + neighbors" with probability $p$ add a new edge $(u, w)$ with + randomly-chosen existing node $w$. In contrast with + :func:`watts_strogatz_graph`, no edges are removed. + + See Also + -------- + watts_strogatz_graph() + + References + ---------- + .. [1] M. E. J. Newman and D. J. Watts, + Renormalization group analysis of the small-world network model, + Physics Letters A, 263, 341, 1999. + https://doi.org/10.1016/S0375-9601(99)00757-4 + """ + if k > n: + raise nx.NetworkXError("k>=n, choose smaller k or larger n") + + # If k == n the graph return is a complete graph + if k == n: + return nx.complete_graph(n) + + G = empty_graph(n) + nlist = list(G.nodes()) + fromv = nlist + # connect the k/2 neighbors + for j in range(1, k // 2 + 1): + tov = fromv[j:] + fromv[0:j] # the first j are now last + for i in range(len(fromv)): + G.add_edge(fromv[i], tov[i]) + # for each edge u-v, with probability p, randomly select existing + # node w and add new edge u-w + e = list(G.edges()) + for (u, v) in e: + if seed.random() < p: + w = seed.choice(nlist) + # no self-loops and reject if edge u-w exists + # is that the correct NWS model? + while w == u or G.has_edge(u, w): + w = seed.choice(nlist) + if G.degree(u) >= n - 1: + break # skip this rewiring + else: + G.add_edge(u, w) + return G + + +@py_random_state(3) +def watts_strogatz_graph(n, k, p, seed=None): + """Returns a Watts–Strogatz small-world graph. + + Parameters + ---------- + n : int + The number of nodes + k : int + Each node is joined with its `k` nearest neighbors in a ring + topology. + p : float + The probability of rewiring each edge + seed : integer, random_state, or None (default) + Indicator of random number generation state. + See :ref:`Randomness<randomness>`. + + See Also + -------- + newman_watts_strogatz_graph() + connected_watts_strogatz_graph() + + Notes + ----- + First create a ring over $n$ nodes [1]_. Then each node in the ring is joined + to its $k$ nearest neighbors (or $k - 1$ neighbors if $k$ is odd). + Then shortcuts are created by replacing some edges as follows: for each + edge $(u, v)$ in the underlying "$n$-ring with $k$ nearest neighbors" + with probability $p$ replace it with a new edge $(u, w)$ with uniformly + random choice of existing node $w$. + + In contrast with :func:`newman_watts_strogatz_graph`, the random rewiring + does not increase the number of edges. The rewired graph is not guaranteed + to be connected as in :func:`connected_watts_strogatz_graph`. + + References + ---------- + .. [1] Duncan J. Watts and Steven H. Strogatz, + Collective dynamics of small-world networks, + Nature, 393, pp. 440--442, 1998. + """ + if k > n: + raise nx.NetworkXError("k>n, choose smaller k or larger n") + + # If k == n, the graph is complete not Watts-Strogatz + if k == n: + return nx.complete_graph(n) + + G = nx.Graph() + nodes = list(range(n)) # nodes are labeled 0 to n-1 + # connect each node to k/2 neighbors + for j in range(1, k // 2 + 1): + targets = nodes[j:] + nodes[0:j] # first j nodes are now last in list + G.add_edges_from(zip(nodes, targets)) + # rewire edges from each node + # loop over all nodes in order (label) and neighbors in order (distance) + # no self loops or multiple edges allowed + for j in range(1, k // 2 + 1): # outer loop is neighbors + targets = nodes[j:] + nodes[0:j] # first j nodes are now last in list + # inner loop in node order + for u, v in zip(nodes, targets): + if seed.random() < p: + w = seed.choice(nodes) + # Enforce no self-loops or multiple edges + while w == u or G.has_edge(u, w): + w = seed.choice(nodes) + if G.degree(u) >= n - 1: + break # skip this rewiring + else: + G.remove_edge(u, v) + G.add_edge(u, w) + return G + + +@py_random_state(4) +def connected_watts_strogatz_graph(n, k, p, tries=100, seed=None): + """Returns a connected Watts–Strogatz small-world graph. + + Attempts to generate a connected graph by repeated generation of + Watts–Strogatz small-world graphs. An exception is raised if the maximum + number of tries is exceeded. + + Parameters + ---------- + n : int + The number of nodes + k : int + Each node is joined with its `k` nearest neighbors in a ring + topology. + p : float + The probability of rewiring each edge + tries : int + Number of attempts to generate a connected graph. + seed : integer, random_state, or None (default) + Indicator of random number generation state. + See :ref:`Randomness<randomness>`. + + Notes + ----- + First create a ring over $n$ nodes [1]_. Then each node in the ring is joined + to its $k$ nearest neighbors (or $k - 1$ neighbors if $k$ is odd). + Then shortcuts are created by replacing some edges as follows: for each + edge $(u, v)$ in the underlying "$n$-ring with $k$ nearest neighbors" + with probability $p$ replace it with a new edge $(u, w)$ with uniformly + random choice of existing node $w$. + The entire process is repeated until a connected graph results. + + See Also + -------- + newman_watts_strogatz_graph() + watts_strogatz_graph() + + References + ---------- + .. [1] Duncan J. Watts and Steven H. Strogatz, + Collective dynamics of small-world networks, + Nature, 393, pp. 440--442, 1998. + """ + for i in range(tries): + # seed is an RNG so should change sequence each call + G = watts_strogatz_graph(n, k, p, seed) + if nx.is_connected(G): + return G + raise nx.NetworkXError("Maximum number of tries exceeded") + + +@py_random_state(2) +def random_regular_graph(d, n, seed=None): + r"""Returns a random $d$-regular graph on $n$ nodes. + + The resulting graph has no self-loops or parallel edges. + + Parameters + ---------- + d : int + The degree of each node. + n : integer + The number of nodes. The value of $n \times d$ must be even. + seed : integer, random_state, or None (default) + Indicator of random number generation state. + See :ref:`Randomness<randomness>`. + + Notes + ----- + The nodes are numbered from $0$ to $n - 1$. + + Kim and Vu's paper [2]_ shows that this algorithm samples in an + asymptotically uniform way from the space of random graphs when + $d = O(n^{1 / 3 - \epsilon})$. + + Raises + ------ + + NetworkXError + If $n \times d$ is odd or $d$ is greater than or equal to $n$. + + References + ---------- + .. [1] A. Steger and N. Wormald, + Generating random regular graphs quickly, + Probability and Computing 8 (1999), 377-396, 1999. + http://citeseer.ist.psu.edu/steger99generating.html + + .. [2] Jeong Han Kim and Van H. Vu, + Generating random regular graphs, + Proceedings of the thirty-fifth ACM symposium on Theory of computing, + San Diego, CA, USA, pp 213--222, 2003. + http://portal.acm.org/citation.cfm?id=780542.780576 + """ + if (n * d) % 2 != 0: + raise nx.NetworkXError("n * d must be even") + + if not 0 <= d < n: + raise nx.NetworkXError("the 0 <= d < n inequality must be satisfied") + + if d == 0: + return empty_graph(n) + + def _suitable(edges, potential_edges): + # Helper subroutine to check if there are suitable edges remaining + # If False, the generation of the graph has failed + if not potential_edges: + return True + for s1 in potential_edges: + for s2 in potential_edges: + # Two iterators on the same dictionary are guaranteed + # to visit it in the same order if there are no + # intervening modifications. + if s1 == s2: + # Only need to consider s1-s2 pair one time + break + if s1 > s2: + s1, s2 = s2, s1 + if (s1, s2) not in edges: + return True + return False + + def _try_creation(): + # Attempt to create an edge set + + edges = set() + stubs = list(range(n)) * d + + while stubs: + potential_edges = defaultdict(lambda: 0) + seed.shuffle(stubs) + stubiter = iter(stubs) + for s1, s2 in zip(stubiter, stubiter): + if s1 > s2: + s1, s2 = s2, s1 + if s1 != s2 and ((s1, s2) not in edges): + edges.add((s1, s2)) + else: + potential_edges[s1] += 1 + potential_edges[s2] += 1 + + if not _suitable(edges, potential_edges): + return None # failed to find suitable edge set + + stubs = [ + node + for node, potential in potential_edges.items() + for _ in range(potential) + ] + return edges + + # Even though a suitable edge set exists, + # the generation of such a set is not guaranteed. + # Try repeatedly to find one. + edges = _try_creation() + while edges is None: + edges = _try_creation() + + G = nx.Graph() + G.add_edges_from(edges) + + return G + + +def _random_subset(seq, m, rng): + """ Return m unique elements from seq. + + This differs from random.sample which can return repeated + elements if seq holds repeated elements. + + Note: rng is a random.Random or numpy.random.RandomState instance. + """ + targets = set() + while len(targets) < m: + x = rng.choice(seq) + targets.add(x) + return targets + + +@py_random_state(2) +def barabasi_albert_graph(n, m, seed=None): + """Returns a random graph according to the Barabási–Albert preferential + attachment model. + + A graph of $n$ nodes is grown by attaching new nodes each with $m$ + edges that are preferentially attached to existing nodes with high degree. + + Parameters + ---------- + n : int + Number of nodes + m : int + Number of edges to attach from a new node to existing nodes + seed : integer, random_state, or None (default) + Indicator of random number generation state. + See :ref:`Randomness<randomness>`. + + Returns + ------- + G : Graph + + Raises + ------ + NetworkXError + If `m` does not satisfy ``1 <= m < n``. + + References + ---------- + .. [1] A. L. Barabási and R. Albert "Emergence of scaling in + random networks", Science 286, pp 509-512, 1999. + """ + + if m < 1 or m >= n: + raise nx.NetworkXError( + f"Barabási–Albert network must have m >= 1 and m < n, m = {m}, n = {n}" + ) + + # Add m initial nodes (m0 in barabasi-speak) + G = empty_graph(m) + # Target nodes for new edges + targets = list(range(m)) + # List of existing nodes, with nodes repeated once for each adjacent edge + repeated_nodes = [] + # Start adding the other n-m nodes. The first node is m. + source = m + while source < n: + # Add edges to m nodes from the source. + G.add_edges_from(zip([source] * m, targets)) + # Add one node to the list for each new edge just created. + repeated_nodes.extend(targets) + # And the new node "source" has m edges to add to the list. + repeated_nodes.extend([source] * m) + # Now choose m unique nodes from the existing nodes + # Pick uniformly from repeated_nodes (preferential attachment) + targets = _random_subset(repeated_nodes, m, seed) + source += 1 + return G + + +@py_random_state(4) +def dual_barabasi_albert_graph(n, m1, m2, p, seed=None): + """Returns a random graph according to the dual Barabási–Albert preferential + attachment model. + + A graph of $n$ nodes is grown by attaching new nodes each with either $m_1$ + edges (with probability $p$) or $m_2$ edges (with probability $1-p$) that + are preferentially attached to existing nodes with high degree. + + Parameters + ---------- + n : int + Number of nodes + m1 : int + Number of edges to attach from a new node to existing nodes with probability $p$ + m2 : int + Number of edges to attach from a new node to existing nodes with probability $1-p$ + p : float + The probability of attaching $m_1$ edges (as opposed to $m_2$ edges) + seed : integer, random_state, or None (default) + Indicator of random number generation state. + See :ref:`Randomness<randomness>`. + + Returns + ------- + G : Graph + + Raises + ------ + NetworkXError + If `m1` and `m2` do not satisfy ``1 <= m1,m2 < n`` or `p` does not satisfy ``0 <= p <= 1``. + + References + ---------- + .. [1] N. Moshiri "The dual-Barabasi-Albert model", arXiv:1810.10538. + """ + + if m1 < 1 or m1 >= n: + raise nx.NetworkXError( + f"Dual Barabási–Albert network must have m1 >= 1 and m1 < n, m1 = {m1}, n = {n}" + ) + if m2 < 1 or m2 >= n: + raise nx.NetworkXError( + f"Dual Barabási–Albert network must have m2 >= 1 and m2 < n, m2 = {m2}, n = {n}" + ) + if p < 0 or p > 1: + raise nx.NetworkXError( + f"Dual Barabási–Albert network must have 0 <= p <= 1, p = {p}" + ) + + # For simplicity, if p == 0 or 1, just return BA + if p == 1: + return barabasi_albert_graph(n, m1, seed) + elif p == 0: + return barabasi_albert_graph(n, m2, seed) + + # Add max(m1,m2) initial nodes (m0 in barabasi-speak) + G = empty_graph(max(m1, m2)) + # Target nodes for new edges + targets = list(range(max(m1, m2))) + # List of existing nodes, with nodes repeated once for each adjacent edge + repeated_nodes = [] + # Start adding the remaining nodes. + source = max(m1, m2) + # Pick which m to use first time (m1 or m2) + if seed.random() < p: + m = m1 + else: + m = m2 + while source < n: + # Add edges to m nodes from the source. + G.add_edges_from(zip([source] * m, targets)) + # Add one node to the list for each new edge just created. + repeated_nodes.extend(targets) + # And the new node "source" has m edges to add to the list. + repeated_nodes.extend([source] * m) + # Pick which m to use next time (m1 or m2) + if seed.random() < p: + m = m1 + else: + m = m2 + # Now choose m unique nodes from the existing nodes + # Pick uniformly from repeated_nodes (preferential attachment) + targets = _random_subset(repeated_nodes, m, seed) + source += 1 + return G + + +@py_random_state(4) +def extended_barabasi_albert_graph(n, m, p, q, seed=None): + """Returns an extended Barabási–Albert model graph. + + An extended Barabási–Albert model graph is a random graph constructed + using preferential attachment. The extended model allows new edges, + rewired edges or new nodes. Based on the probabilities $p$ and $q$ + with $p + q < 1$, the growing behavior of the graph is determined as: + + 1) With $p$ probability, $m$ new edges are added to the graph, + starting from randomly chosen existing nodes and attached preferentially at the other end. + + 2) With $q$ probability, $m$ existing edges are rewired + by randomly choosing an edge and rewiring one end to a preferentially chosen node. + + 3) With $(1 - p - q)$ probability, $m$ new nodes are added to the graph + with edges attached preferentially. + + When $p = q = 0$, the model behaves just like the Barabási–Alber model. + + Parameters + ---------- + n : int + Number of nodes + m : int + Number of edges with which a new node attaches to existing nodes + p : float + Probability value for adding an edge between existing nodes. p + q < 1 + q : float + Probability value of rewiring of existing edges. p + q < 1 + seed : integer, random_state, or None (default) + Indicator of random number generation state. + See :ref:`Randomness<randomness>`. + + Returns + ------- + G : Graph + + Raises + ------ + NetworkXError + If `m` does not satisfy ``1 <= m < n`` or ``1 >= p + q`` + + References + ---------- + .. [1] Albert, R., & Barabási, A. L. (2000) + Topology of evolving networks: local events and universality + Physical review letters, 85(24), 5234. + """ + if m < 1 or m >= n: + msg = f"Extended Barabasi-Albert network needs m>=1 and m<n, m={m}, n={n}" + raise nx.NetworkXError(msg) + if p + q >= 1: + msg = f"Extended Barabasi-Albert network needs p + q <= 1, p={p}, q={q}" + raise nx.NetworkXError(msg) + + # Add m initial nodes (m0 in barabasi-speak) + G = empty_graph(m) + + # List of nodes to represent the preferential attachment random selection. + # At the creation of the graph, all nodes are added to the list + # so that even nodes that are not connected have a chance to get selected, + # for rewiring and adding of edges. + # With each new edge, nodes at the ends of the edge are added to the list. + attachment_preference = [] + attachment_preference.extend(range(m)) + + # Start adding the other n-m nodes. The first node is m. + new_node = m + while new_node < n: + a_probability = seed.random() + + # Total number of edges of a Clique of all the nodes + clique_degree = len(G) - 1 + clique_size = (len(G) * clique_degree) / 2 + + # Adding m new edges, if there is room to add them + if a_probability < p and G.size() <= clique_size - m: + # Select the nodes where an edge can be added + elligible_nodes = [nd for nd, deg in G.degree() if deg < clique_degree] + for i in range(m): + # Choosing a random source node from elligible_nodes + src_node = seed.choice(elligible_nodes) + + # Picking a possible node that is not 'src_node' or + # neighbor with 'src_node', with preferential attachment + prohibited_nodes = list(G[src_node]) + prohibited_nodes.append(src_node) + # This will raise an exception if the sequence is empty + dest_node = seed.choice( + [nd for nd in attachment_preference if nd not in prohibited_nodes] + ) + # Adding the new edge + G.add_edge(src_node, dest_node) + + # Appending both nodes to add to their preferential attachment + attachment_preference.append(src_node) + attachment_preference.append(dest_node) + + # Adjusting the elligible nodes. Degree may be saturated. + if G.degree(src_node) == clique_degree: + elligible_nodes.remove(src_node) + if ( + G.degree(dest_node) == clique_degree + and dest_node in elligible_nodes + ): + elligible_nodes.remove(dest_node) + + # Rewiring m edges, if there are enough edges + elif p <= a_probability < (p + q) and m <= G.size() < clique_size: + # Selecting nodes that have at least 1 edge but that are not + # fully connected to ALL other nodes (center of star). + # These nodes are the pivot nodes of the edges to rewire + elligible_nodes = [nd for nd, deg in G.degree() if 0 < deg < clique_degree] + for i in range(m): + # Choosing a random source node + node = seed.choice(elligible_nodes) + + # The available nodes do have a neighbor at least. + neighbor_nodes = list(G[node]) + + # Choosing the other end that will get dettached + src_node = seed.choice(neighbor_nodes) + + # Picking a target node that is not 'node' or + # neighbor with 'node', with preferential attachment + neighbor_nodes.append(node) + dest_node = seed.choice( + [nd for nd in attachment_preference if nd not in neighbor_nodes] + ) + # Rewire + G.remove_edge(node, src_node) + G.add_edge(node, dest_node) + + # Adjusting the preferential attachment list + attachment_preference.remove(src_node) + attachment_preference.append(dest_node) + + # Adjusting the elligible nodes. + # nodes may be saturated or isolated. + if G.degree(src_node) == 0 and src_node in elligible_nodes: + elligible_nodes.remove(src_node) + if dest_node in elligible_nodes: + if G.degree(dest_node) == clique_degree: + elligible_nodes.remove(dest_node) + else: + if G.degree(dest_node) == 1: + elligible_nodes.append(dest_node) + + # Adding new node with m edges + else: + # Select the edges' nodes by preferential attachment + targets = _random_subset(attachment_preference, m, seed) + G.add_edges_from(zip([new_node] * m, targets)) + + # Add one node to the list for each new edge just created. + attachment_preference.extend(targets) + # The new node has m edges to it, plus itself: m + 1 + attachment_preference.extend([new_node] * (m + 1)) + new_node += 1 + return G + + +@py_random_state(3) +def powerlaw_cluster_graph(n, m, p, seed=None): + """Holme and Kim algorithm for growing graphs with powerlaw + degree distribution and approximate average clustering. + + Parameters + ---------- + n : int + the number of nodes + m : int + the number of random edges to add for each new node + p : float, + Probability of adding a triangle after adding a random edge + seed : integer, random_state, or None (default) + Indicator of random number generation state. + See :ref:`Randomness<randomness>`. + + Notes + ----- + The average clustering has a hard time getting above a certain + cutoff that depends on `m`. This cutoff is often quite low. The + transitivity (fraction of triangles to possible triangles) seems to + decrease with network size. + + It is essentially the Barabási–Albert (BA) growth model with an + extra step that each random edge is followed by a chance of + making an edge to one of its neighbors too (and thus a triangle). + + This algorithm improves on BA in the sense that it enables a + higher average clustering to be attained if desired. + + It seems possible to have a disconnected graph with this algorithm + since the initial `m` nodes may not be all linked to a new node + on the first iteration like the BA model. + + Raises + ------ + NetworkXError + If `m` does not satisfy ``1 <= m <= n`` or `p` does not + satisfy ``0 <= p <= 1``. + + References + ---------- + .. [1] P. Holme and B. J. Kim, + "Growing scale-free networks with tunable clustering", + Phys. Rev. E, 65, 026107, 2002. + """ + + if m < 1 or n < m: + raise nx.NetworkXError(f"NetworkXError must have m>1 and m<n, m={m},n={n}") + + if p > 1 or p < 0: + raise nx.NetworkXError(f"NetworkXError p must be in [0,1], p={p}") + + G = empty_graph(m) # add m initial nodes (m0 in barabasi-speak) + repeated_nodes = list(G.nodes()) # list of existing nodes to sample from + # with nodes repeated once for each adjacent edge + source = m # next node is m + while source < n: # Now add the other n-1 nodes + possible_targets = _random_subset(repeated_nodes, m, seed) + # do one preferential attachment for new node + target = possible_targets.pop() + G.add_edge(source, target) + repeated_nodes.append(target) # add one node to list for each new link + count = 1 + while count < m: # add m-1 more new links + if seed.random() < p: # clustering step: add triangle + neighborhood = [ + nbr + for nbr in G.neighbors(target) + if not G.has_edge(source, nbr) and not nbr == source + ] + if neighborhood: # if there is a neighbor without a link + nbr = seed.choice(neighborhood) + G.add_edge(source, nbr) # add triangle + repeated_nodes.append(nbr) + count = count + 1 + continue # go to top of while loop + # else do preferential attachment step if above fails + target = possible_targets.pop() + G.add_edge(source, target) + repeated_nodes.append(target) + count = count + 1 + + repeated_nodes.extend([source] * m) # add source node to list m times + source += 1 + return G + + +@py_random_state(3) +def random_lobster(n, p1, p2, seed=None): + """Returns a random lobster graph. + + A lobster is a tree that reduces to a caterpillar when pruning all + leaf nodes. A caterpillar is a tree that reduces to a path graph + when pruning all leaf nodes; setting `p2` to zero produces a caterpillar. + + This implementation iterates on the probabilities `p1` and `p2` to add + edges at levels 1 and 2, respectively. Graphs are therefore constructed + iteratively with uniform randomness at each level rather than being selected + uniformly at random from the set of all possible lobsters. + + Parameters + ---------- + n : int + The expected number of nodes in the backbone + p1 : float + Probability of adding an edge to the backbone + p2 : float + Probability of adding an edge one level beyond backbone + seed : integer, random_state, or None (default) + Indicator of random number generation state. + See :ref:`Randomness<randomness>`. + + Raises + ------ + NetworkXError + If `p1` or `p2` parameters are >= 1 because the while loops would never finish. + """ + p1, p2 = abs(p1), abs(p2) + if any([p >= 1 for p in [p1, p2]]): + raise nx.NetworkXError("Probability values for `p1` and `p2` must both be < 1.") + + # a necessary ingredient in any self-respecting graph library + llen = int(2 * seed.random() * n + 0.5) + L = path_graph(llen) + # build caterpillar: add edges to path graph with probability p1 + current_node = llen - 1 + for n in range(llen): + while seed.random() < p1: # add fuzzy caterpillar parts + current_node += 1 + L.add_edge(n, current_node) + cat_node = current_node + while seed.random() < p2: # add crunchy lobster bits + current_node += 1 + L.add_edge(cat_node, current_node) + return L # voila, un lobster! + + +@py_random_state(1) +def random_shell_graph(constructor, seed=None): + """Returns a random shell graph for the constructor given. + + Parameters + ---------- + constructor : list of three-tuples + Represents the parameters for a shell, starting at the center + shell. Each element of the list must be of the form `(n, m, + d)`, where `n` is the number of nodes in the shell, `m` is + the number of edges in the shell, and `d` is the ratio of + inter-shell (next) edges to intra-shell edges. If `d` is zero, + there will be no intra-shell edges, and if `d` is one there + will be all possible intra-shell edges. + seed : integer, random_state, or None (default) + Indicator of random number generation state. + See :ref:`Randomness<randomness>`. + + Examples + -------- + >>> constructor = [(10, 20, 0.8), (20, 40, 0.8)] + >>> G = nx.random_shell_graph(constructor) + + """ + G = empty_graph(0) + + glist = [] + intra_edges = [] + nnodes = 0 + # create gnm graphs for each shell + for (n, m, d) in constructor: + inter_edges = int(m * d) + intra_edges.append(m - inter_edges) + g = nx.convert_node_labels_to_integers( + gnm_random_graph(n, inter_edges, seed=seed), first_label=nnodes + ) + glist.append(g) + nnodes += n + G = nx.operators.union(G, g) + + # connect the shells randomly + for gi in range(len(glist) - 1): + nlist1 = list(glist[gi]) + nlist2 = list(glist[gi + 1]) + total_edges = intra_edges[gi] + edge_count = 0 + while edge_count < total_edges: + u = seed.choice(nlist1) + v = seed.choice(nlist2) + if u == v or G.has_edge(u, v): + continue + else: + G.add_edge(u, v) + edge_count = edge_count + 1 + return G + + +@py_random_state(2) +def random_powerlaw_tree(n, gamma=3, seed=None, tries=100): + """Returns a tree with a power law degree distribution. + + Parameters + ---------- + n : int + The number of nodes. + gamma : float + Exponent of the power law. + seed : integer, random_state, or None (default) + Indicator of random number generation state. + See :ref:`Randomness<randomness>`. + tries : int + Number of attempts to adjust the sequence to make it a tree. + + Raises + ------ + NetworkXError + If no valid sequence is found within the maximum number of + attempts. + + Notes + ----- + A trial power law degree sequence is chosen and then elements are + swapped with new elements from a powerlaw distribution until the + sequence makes a tree (by checking, for example, that the number of + edges is one smaller than the number of nodes). + + """ + # This call may raise a NetworkXError if the number of tries is succeeded. + seq = random_powerlaw_tree_sequence(n, gamma=gamma, seed=seed, tries=tries) + G = degree_sequence_tree(seq) + return G + + +@py_random_state(2) +def random_powerlaw_tree_sequence(n, gamma=3, seed=None, tries=100): + """Returns a degree sequence for a tree with a power law distribution. + + Parameters + ---------- + n : int, + The number of nodes. + gamma : float + Exponent of the power law. + seed : integer, random_state, or None (default) + Indicator of random number generation state. + See :ref:`Randomness<randomness>`. + tries : int + Number of attempts to adjust the sequence to make it a tree. + + Raises + ------ + NetworkXError + If no valid sequence is found within the maximum number of + attempts. + + Notes + ----- + A trial power law degree sequence is chosen and then elements are + swapped with new elements from a power law distribution until + the sequence makes a tree (by checking, for example, that the number of + edges is one smaller than the number of nodes). + + """ + # get trial sequence + z = nx.utils.powerlaw_sequence(n, exponent=gamma, seed=seed) + # round to integer values in the range [0,n] + zseq = [min(n, max(int(round(s)), 0)) for s in z] + + # another sequence to swap values from + z = nx.utils.powerlaw_sequence(tries, exponent=gamma, seed=seed) + # round to integer values in the range [0,n] + swap = [min(n, max(int(round(s)), 0)) for s in z] + + for deg in swap: + # If this degree sequence can be the degree sequence of a tree, return + # it. It can be a tree if the number of edges is one fewer than the + # number of nodes, or in other words, `n - sum(zseq) / 2 == 1`. We + # use an equivalent condition below that avoids floating point + # operations. + if 2 * n - sum(zseq) == 2: + return zseq + index = seed.randint(0, n - 1) + zseq[index] = swap.pop() + + raise nx.NetworkXError( + f"Exceeded max ({tries}) attempts for a valid tree sequence." + ) + + +@py_random_state(3) +def random_kernel_graph(n, kernel_integral, kernel_root=None, seed=None): + r"""Returns an random graph based on the specified kernel. + + The algorithm chooses each of the $[n(n-1)]/2$ possible edges with + probability specified by a kernel $\kappa(x,y)$ [1]_. The kernel + $\kappa(x,y)$ must be a symmetric (in $x,y$), non-negative, + bounded function. + + Parameters + ---------- + n : int + The number of nodes + kernal_integral : function + Function that returns the definite integral of the kernel $\kappa(x,y)$, + $F(y,a,b) := \int_a^b \kappa(x,y)dx$ + kernel_root: function (optional) + Function that returns the root $b$ of the equation $F(y,a,b) = r$. + If None, the root is found using :func:`scipy.optimize.brentq` + (this requires SciPy). + seed : integer, random_state, or None (default) + Indicator of random number generation state. + See :ref:`Randomness<randomness>`. + + Notes + ----- + The kernel is specified through its definite integral which must be + provided as one of the arguments. If the integral and root of the + kernel integral can be found in $O(1)$ time then this algorithm runs in + time $O(n+m)$ where m is the expected number of edges [2]_. + + The nodes are set to integers from $0$ to $n-1$. + + Examples + -------- + Generate an Erdős–Rényi random graph $G(n,c/n)$, with kernel + $\kappa(x,y)=c$ where $c$ is the mean expected degree. + + >>> def integral(u, w, z): + ... return c * (z - w) + >>> def root(u, w, r): + ... return r / c + w + >>> c = 1 + >>> graph = nx.random_kernel_graph(1000, integral, root) + + See Also + -------- + gnp_random_graph + expected_degree_graph + + References + ---------- + .. [1] Bollobás, Béla, Janson, S. and Riordan, O. + "The phase transition in inhomogeneous random graphs", + *Random Structures Algorithms*, 31, 3--122, 2007. + + .. [2] Hagberg A, Lemons N (2015), + "Fast Generation of Sparse Random Kernel Graphs". + PLoS ONE 10(9): e0135177, 2015. doi:10.1371/journal.pone.0135177 + """ + if kernel_root is None: + import scipy.optimize as optimize + + def kernel_root(y, a, r): + def my_function(b): + return kernel_integral(y, a, b) - r + + return optimize.brentq(my_function, a, 1) + + graph = nx.Graph() + graph.add_nodes_from(range(n)) + (i, j) = (1, 1) + while i < n: + r = -math.log(1 - seed.random()) # (1-seed.random()) in (0, 1] + if kernel_integral(i / n, j / n, 1) <= r: + i, j = i + 1, i + 1 + else: + j = int(math.ceil(n * kernel_root(i / n, j / n, r))) + graph.add_edge(i - 1, j - 1) + return graph