lib/graph.njae/graph.rb

   1 require 'ostruct'
   2
   3 # A simple graph library
   4
   5 module GraphNjae
   6
   7   # A container for all the parts of a graph.  The graph can have arbitrary attributes,
   8   # treated as method names.
   9   class Graph < OpenStruct
  10     def initialize(values = {})
  11       super(values)
  12       self.edges = Array.new
  13       self.vertices = Array.new
  14       self
  15     end
  16
  17     # Add a Vertex or Edge to the graph.
  18     def <<(other)
  19       if other.class.ancestors.include? Vertex
  20         self.vertices << other
  21       elsif other.class.ancestors.include? Edge
  22         self.edges << other
  23       end
  24       self
  25     end
  26
  27     # Connects two vertices, creating and storing a new edge
  28     # Also adds the vertices, unless they're already in the graph
  29     def connect(vertex1, vertex2)
  30       self.vertices << vertex1 unless self.vertices.include? vertex1
  31       self.vertices << vertex2 unless self.vertices.include? vertex2
  32       edge = Edge.new
  33       self.edges << edge
  34       edge << vertex1 << vertex2
  35     end
  36
  37     # Form a product graph of this graph and the other.
  38     # Return the product graph.
  39     def product(other)
  40       product_graph = Graph.new
  41       self.vertices.each do |v1|
  42         other.vertices.each do |v2|
  43           product_graph << Vertex.new({:g1_vertex => v1, :g2_vertex => v2})
  44         end
  45       end
  46       self.edges.each do |e1|
  47         e1_vertices = e1.vertices
  48         other.edges.each do |e2|
  49           e2_vertices = e2.vertices
  50           source = product_graph.vertices.find {|v| v.g1_vertex == e1_vertices[0] and v.g2_vertex == e2_vertices[0]}
  51           destination = product_graph.vertices.find {|v| v.g1_vertex == e1_vertices[1] and v.g2_vertex == e2_vertices[1]}
  52           product_graph.connect source, destination
  53           source = product_graph.vertices.find {|v| v.g1_vertex == e1_vertices[0] and v.g2_vertex == e2_vertices[1]}
  54           destination = product_graph.vertices.find {|v| v.g1_vertex == e1_vertices[1] and v.g2_vertex == e2_vertices[0]}
  55           product_graph.connect source, destination
  56         end
  57       end
  58       product_graph
  59     end
  60
  61
  62     def initial_similarity
  63       self.vertices.each do |v|
  64         if block_given?
  65           v.initial_similarity = yield v
  66         else
  67           v.initial_similarity = 1.0
  68         end
  69         v.similarity = v.initial_similarity
  70       end
  71     end
  72
  73     # Performs similarity flooding on a graph
  74     # Assumes that the initial similarity has already been calculated
  75     def similarity_flood(opts = {})
  76       max_iterations = opts[:iterations] || 100
  77       max_residual = opts[:max_residual] || 0.001
  78       iteration = 1
  79       residual = max_residual + 1
  80       while residual > max_residual and iteration <= max_iterations
  81         self.vertices.each do |v|
  82           v.last_similarity = v.similarity
  83         end
  84         self.vertices.each do |v|
  85            n = v.neighbours.length
  86            v.neighbours.each do |neighbour|
  87              neighbour.similarity += v.last_similarity / n
  88            end
  89         end
  90         max_similarity = vertices.max {|v, w| v.similarity <=> w.similarity}.similarity
  91         self.vertices.each do |v|
  92           v.similarity = v.similarity / max_similarity
  93         end
  94         residual = Math.sqrt(self.vertices.reduce(0) {|a, v| a += (v.similarity - v.last_similarity) ** 2})
  95         iteration += 1
  96       end
  97
  98     end
  99
 100   end # class
 101 end