Class: MHL::RechenbergController

Inherits:
Object
  • Object
show all
Defined in:
lib/mhl/rechenberg_controller.rb

Constant Summary collapse

DEFAULT_THRESHOLD = 
1.0/5.0
TAU = 
1.10
P_M_MAX = 
0.99
P_M_MIN = 
0.01

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(generations = 5, threshold = DEFAULT_THRESHOLD, logger = nil) ⇒ RechenbergController

Returns a new instance of RechenbergController.



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# File 'lib/mhl/rechenberg_controller.rb', line 11

def initialize(generations=5, threshold=DEFAULT_THRESHOLD, logger=nil)
  unless threshold > 0.0 and threshold < 1.0
    raise ArgumentError, "The threshold parameter must be in the (0.0,1.0) range!"
  end
  @generations = generations
  @threshold   = threshold
  @logger      = logger
  @history     = []
end

Instance Attribute Details

#generations ⇒ Object (readonly)

Returns the value of attribute generations.



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# File 'lib/mhl/rechenberg_controller.rb', line 9

def generations
  @generations
end

#threshold ⇒ Object (readonly)

Returns the value of attribute threshold.



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# File 'lib/mhl/rechenberg_controller.rb', line 9

def threshold
  @threshold
end

Instance Method Details

#call(solver, best) ⇒ Object 



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# File 'lib/mhl/rechenberg_controller.rb', line 21

def call(solver, best)
  @history << best

  if @history.size > @generations
    # calculate improvement ratio
    res = @history.each_cons(2).inject(0) {|s,x| s += 1 if x[1][:fitness] > x[0][:fitness]; s } / (@history.size - 1).to_f
    if res > @threshold
      # we had enough improvements - decrease impact of mutation
      # increase mutation probability by 5% or to P_M_MAX
      old_p_m = solver.mutation_probability
      new_p_m = [ old_p_m * TAU, P_M_MAX ].min
      @logger.info "increasing mutation_probability from #{old_p_m} to #{new_p_m}" if @logger
      solver.mutation_probability = new_p_m
    else
      # we didn't have enough improvements - increase impact of mutation
      # decrease mutation probability by 5% or to P_M_MAX
      old_p_m = solver.mutation_probability
      new_p_m = [ old_p_m / TAU, P_M_MIN ].max
      @logger.info "decreasing mutation_probability from #{old_p_m} to #{new_p_m}" if @logger
      solver.mutation_probability = new_p_m
    end

    # reset
    @history.shift(@history.size-1)
  end
end