Class: Lernen::Algorithm::KearnsVazirani::DiscriminationTree

Inherits:
Object
  • Object
show all
Defined in:
lib/lernen/algorithm/kearns_vazirani/discrimination_tree.rb

Overview

DiscriminationTree is an implementation of discrimination tree data structure.

This data structure is used for Kearns-Vazirani algorithm.

Constant Summary collapse

Node = 
Data.define(:suffix, :branch)
Leaf = 
Data.define(:prefix)

Instance Method Summary collapse

Constructor Details

#initialize(alphabet, sul, cex:, automaton_type:, cex_processing:) ⇒ DiscriminationTree

: (

  Array[In] alphabet,
  System::SUL[In, Out] sul,
  cex: Array[In],
  automaton_type: :dfa | :mealy | :moore,
  cex_processing: cex_processing_method
) -> void



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# File 'lib/lernen/algorithm/kearns_vazirani/discrimination_tree.rb', line 50

def initialize(alphabet, sul, cex:, automaton_type:, cex_processing:)
  @alphabet = alphabet
  @sul = sul
  @automaton_type = automaton_type
  @cex_processing = cex_processing

  @path_hash = {}

  case @automaton_type
  in :dfa | :moore
    @root = Node[[], {}]

    empty_out = sul.query_empty
    @root.branch[empty_out] = Leaf[[]]
    @path_hash[[]] = [empty_out]

    cex_out = sul.query_last(cex)
    @root.branch[cex_out] = Leaf[cex]
    @path_hash[cex] = [cex_out]
  in :mealy
    prefix = cex[0...-1]
    suffix = [cex.last]
    @root = Node[suffix, {}]

    suffix_out = sul.query_last(suffix)
    @root.branch[suffix_out] = Leaf[[]]
    @path_hash[[]] = [suffix_out]

    cex_out = sul.query_last(cex)
    @root.branch[cex_out] = Leaf[prefix]
    @path_hash[prefix] = [cex_out]
  end
end

Instance Method Details

#build_hypothesis ⇒ Object

Constructs a hypothesis automaton from this discrimination tree.

: () -> [Automaton::TransitionSystem[Integer, In, Out], Hash[Integer, Array]]



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# File 'lib/lernen/algorithm/kearns_vazirani/discrimination_tree.rb', line 111

def build_hypothesis
  transition_function = {}

  queue = []
  prefix_to_state = {}
  state_to_prefix = {}

  queue << []
  prefix_to_state[[]] = prefix_to_state.size
  state_to_prefix[state_to_prefix.size] = []

  until queue.empty?
    prefix = queue.shift
    state = prefix_to_state[prefix]
    @alphabet.each do |input|
      word = prefix + [input]
      next_prefix = sift(word)

      unless prefix_to_state.include?(next_prefix)
        queue << next_prefix
        prefix_to_state[next_prefix] = prefix_to_state.size
        state_to_prefix[state_to_prefix.size] = next_prefix
      end

      next_state = prefix_to_state[next_prefix]
      case @automaton_type
      in :dfa | :moore
        transition_function[[state, input]] = next_state
      in :mealy
        output = @sul.query_last(word)
        transition_function[[state, input]] = [output, next_state]
      end
    end
  end

  automaton =
    case @automaton_type
    in :dfa
      accept_states =
        state_to_prefix.to_a.filter { |(_, prefix)| @path_hash[prefix][0] }.to_set { |(state, _)| state }
      Automaton::DFA.new(0, accept_states, transition_function)
    in :moore
      outputs = state_to_prefix.transform_values { |prefix| @path_hash[prefix][0] }
      Automaton::Moore.new(0, outputs, transition_function)
    in :mealy
      Automaton::Mealy.new(0, transition_function)
    end

  [automaton, state_to_prefix]
end

#refine_hypothesis(cex, hypothesis, state_to_prefix) ⇒ Object

Update this classification tree by the given ‘cex`.

: (

  Array[In] cex,
  Automaton::TransitionSystem[Integer, In, Out] hypothesis,
  Hash[Integer, Array[In]] state_to_prefix
) -> void



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# File 'lib/lernen/algorithm/kearns_vazirani/discrimination_tree.rb', line 169

def refine_hypothesis(cex, hypothesis, state_to_prefix)
  state_to_prefix_lambda = ->(state) { state_to_prefix[state] }
  acex = CexProcessor::PrefixTransformerAcex.new(cex, @sul, hypothesis, state_to_prefix_lambda)

  n = CexProcessor.process(acex, cex_processing: @cex_processing)
  old_prefix = cex[0...n]
  new_input = cex[n]
  new_suffix = cex[n + 1...]

  _, old_state = hypothesis.run(old_prefix) # steep:ignore
  _, replace_state = hypothesis.step(old_state, new_input)

  new_prefix = state_to_prefix[old_state] + [new_input]
  new_out = @sul.query_last(new_prefix + new_suffix) # steep:ignore

  replace_prefix = state_to_prefix[replace_state]
  replace_out = @sul.query_last(replace_prefix + new_suffix) # steep:ignore

  replace_node_path = @path_hash[replace_prefix]
  replace_node_parent = @root
  replace_node = @root.branch[replace_node_path.first] # steep:ignore
  replace_node_path[1..].each do |out| # steep:ignore
    replace_node_parent = replace_node
    replace_node = replace_node.branch[out] # steep:ignore
  end

  new_node = Node[new_suffix, {}] # steep:ignore
  replace_node_parent.branch[replace_node_path.last] = new_node # steep:ignore

  new_node.branch[new_out] = Leaf[new_prefix]
  @path_hash[new_prefix] = replace_node_path + [new_out] # steep:ignore

  new_node.branch[replace_out] = Leaf[replace_prefix]
  @path_hash[replace_prefix] = replace_node_path + [replace_out] # steep:ignore
end

#sift(word) ⇒ Object

Returns a prefix discriminated by ‘word`.

: (Array word) -> Array



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# File 'lib/lernen/algorithm/kearns_vazirani/discrimination_tree.rb', line 87

def sift(word)
  node = @root
  path = []

  until node.is_a?(Leaf)
    full_word = word + node.suffix

    out = @sul.query_last(full_word)
    path << out

    unless node.branch.include?(out)
      node.branch[out] = Leaf[word]
      @path_hash[word] = path
    end

    node = node.branch[out] # steep:ignore
  end

  node.prefix # steep:ignore
end