Mercurial > repos > shellac > sam_consensus_v3
annotate env/lib/python3.9/site-packages/networkx/algorithms/mis.py @ 0:4f3585e2f14b draft default tip
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author | shellac |
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date | Mon, 22 Mar 2021 18:12:50 +0000 |
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1 """ |
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2 Algorithm to find a maximal (not maximum) independent set. |
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3 |
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4 """ |
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5 import networkx as nx |
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6 from networkx.utils import not_implemented_for |
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7 from networkx.utils import py_random_state |
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8 |
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9 __all__ = ["maximal_independent_set"] |
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10 |
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11 |
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12 @py_random_state(2) |
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13 @not_implemented_for("directed") |
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14 def maximal_independent_set(G, nodes=None, seed=None): |
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15 """Returns a random maximal independent set guaranteed to contain |
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16 a given set of nodes. |
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17 |
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18 An independent set is a set of nodes such that the subgraph |
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19 of G induced by these nodes contains no edges. A maximal |
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20 independent set is an independent set such that it is not possible |
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21 to add a new node and still get an independent set. |
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22 |
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23 Parameters |
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24 ---------- |
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25 G : NetworkX graph |
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26 |
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27 nodes : list or iterable |
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28 Nodes that must be part of the independent set. This set of nodes |
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29 must be independent. |
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30 |
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31 seed : integer, random_state, or None (default) |
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32 Indicator of random number generation state. |
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33 See :ref:`Randomness<randomness>`. |
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34 |
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35 Returns |
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36 ------- |
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37 indep_nodes : list |
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38 List of nodes that are part of a maximal independent set. |
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39 |
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40 Raises |
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41 ------ |
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42 NetworkXUnfeasible |
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43 If the nodes in the provided list are not part of the graph or |
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44 do not form an independent set, an exception is raised. |
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45 |
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46 NetworkXNotImplemented |
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47 If `G` is directed. |
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48 |
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49 Examples |
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50 -------- |
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51 >>> G = nx.path_graph(5) |
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52 >>> nx.maximal_independent_set(G) # doctest: +SKIP |
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53 [4, 0, 2] |
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54 >>> nx.maximal_independent_set(G, [1]) # doctest: +SKIP |
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55 [1, 3] |
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56 |
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57 Notes |
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58 ----- |
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59 This algorithm does not solve the maximum independent set problem. |
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60 |
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61 """ |
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62 if not nodes: |
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63 nodes = {seed.choice(list(G))} |
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64 else: |
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65 nodes = set(nodes) |
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66 if not nodes.issubset(G): |
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67 raise nx.NetworkXUnfeasible(f"{nodes} is not a subset of the nodes of G") |
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68 neighbors = set.union(*[set(G.adj[v]) for v in nodes]) |
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69 if set.intersection(neighbors, nodes): |
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70 raise nx.NetworkXUnfeasible(f"{nodes} is not an independent set of G") |
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71 indep_nodes = list(nodes) |
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72 available_nodes = set(G.nodes()).difference(neighbors.union(nodes)) |
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73 while available_nodes: |
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74 node = seed.choice(list(available_nodes)) |
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75 indep_nodes.append(node) |
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76 available_nodes.difference_update(list(G.adj[node]) + [node]) |
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77 return indep_nodes |