Class: Glymour::StructureLearning::LearningNet

Inherits:
Object
  • Object
show all
Includes:
Glymour::Statistics
Defined in:
lib/glymour.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods included from Glymour::Statistics

#coindependent?

Constructor Details

#initialize(variable_container, p_value = 0.05) ⇒ LearningNet

Returns a new instance of LearningNet.



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# File 'lib/glymour.rb', line 139

def initialize(variable_container, p_value = 0.05)
  @net = complete_graph(variable_container.variables).extend(GraphAlgorithms)
  @directed_edges = {}
  @directed_edges.default = []
  @n = -1
  @p_value = p_value
end

Instance Attribute Details

#directed_edges ⇒ Object

Returns the value of attribute directed_edges.



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# File 'lib/glymour.rb', line 136

def directed_edges
  @directed_edges
end

#n ⇒ Object

Returns the value of attribute n.



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# File 'lib/glymour.rb', line 136

def n
  @n
end

#net ⇒ Object

Returns the value of attribute net.



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# File 'lib/glymour.rb', line 136

def net
  @net
end

#p_value ⇒ Object (readonly)

Returns the value of attribute p_value.



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# File 'lib/glymour.rb', line 137

def p_value
  @p_value
end

Instance Method Details

#compatible_orientations ⇒ Object

Gives a list of all orientations of @net compatible with @directed_edges (i.e., all directed acyclic graphs with edge structure given partially by @directed_edges)



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# File 'lib/glymour.rb', line 216

def compatible_orientations
  compat_list = []
  edges = net.edges.extend(PowerSet)
  
  # Every orientation of net corresponds to a subset of its edges
  edges.power_set.each do |subset|
    # Orient edges in subset as source => target, outside of it as target => source
    # Any edges conflicting with directed_edges will be cyclic and therefore not counted
    current_orientation = make_directed(net.vertices, @directed_edges)
    
    edges.each do |e|
      if subset.include? e
        current_orientation.add_edge(e.source, e.target)
      else
        current_orientation.add_edge(e.target, e.source)
      end
    end
    
    compat_list << current_orientation if current_orientation.acyclic?
  end
  
  compat_list
end

#direct_edges ⇒ Object

Direct remaining edges in @net as much as possible



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# File 'lib/glymour.rb', line 194

def direct_edges
  puts "Directing edges where possible..."
  
  net.non_transitive.each do |triple|
    a, b, c = *triple
    
    intersect = (net.adjacent_either(a, c) & net.verts_on_paths(a, c)).extend(PowerSet)
    if intersect.power_set.select {|s| s.include? b}.none? { |subset| 
      coindependent?(p_value, a, c, *subset)
    }
      puts "Adding directed edge #{a.name} => #{b.name}..."
      @directed_edges[a] = (@directed_edges[a] << b).uniq
      
      puts "Adding directed edge #{c.name} => #{b.name}..."
      @directed_edges[c] = (@directed_edges[c] << b).uniq
    end
  end
end

#learn_structure ⇒ Object

Perform the PC algorithm in full



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# File 'lib/glymour.rb', line 178

def learn_structure
  puts "Learning undirected net structure..."
  # Perform step until every pair of adjacent variables is dependent, and
  # set final_net to the _second-to-last_ state of @net
  begin
    puts "n = #{n}"
    final_net = net
    step
  end while n < 1
  
  net = final_net
  
  direct_edges
end

#step ⇒ Object

Perform one step of the PC algorithm



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# File 'lib/glymour.rb', line 148

def step
  any_independent = false
  net.edges.each do |e|
    a, b = e.source, e.target
    intersect = (@net.adjacent_either(a, b) & @net.verts_on_paths(a, b)).extend(PowerSet)
    
    # Is |Aab ^ Uab| > n? 
    if intersect.length <= n
      next
    else
      # Are a and b independent conditioned on any subsets of Aab ^ Uab of cardinality n+1?
      valid_intersects = intersect.power_set.select {|s| s.length == n+1}.reject { |subset| subset.include?(a) || subset.include?(b) }
      if valid_intersects.any? { |subset|
        print "Testing independence between #{a.name} and #{b.name}, conditioning on #{(subset.any? ? subset.map(&:name).join(', ') : 'nothing') + '...'}"
        print (coindependent?(p_value, a, b, *subset) ? "[+]\n" : "[-]\n")
        coindependent?(p_value, a, b, *subset)
      }
        @net = remove_edge(net, e)
        net.edges.each do |e|
          puts "#{e.source.name} => #{e.target.name}"
        end
        any_independent = true
      end
    end
  end
  @n += 1
  any_independent
end