Class: Evolvable::Mutation

Inherits:
Object
  • Object
show all
Extended by:
Forwardable
Defined in:
lib/evolvable/mutation.rb

Overview

Mutation serves the role of increasing genetic variation. When an evolvable undergoes a mutation, one or more of its genes are replaced by newly initialized ones. In effect, a gene mutation invokes a new random outcome from the genetic search space.

Mutation frequency is configurable using the probability and rate parameters.

Examples:

# Show how to initialize/assign population with a specific mutation object

Constant Summary collapse

DEFAULT_PROBABILITY = 
0.03

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(probability: nil, rate: nil) ⇒ Mutation

Initializes a new mutation object.

Keyword arguments:

probability

The probability that a particular instance undergoes a mutation. By default, the probability is 0.03 which translates to 3%. If initialized with a rate, the probability will be 1 which means all genes can undergo mutation, but actual gene mutations will be subject to the given mutation rate.

rate

the rate at which individual genes mutate. The default rate is 0 which, when combined with a non-zero probability (the default), means that one gene for each instance that undergoes mutation will change. If a rate is given, but no probability is given, then the probability will bet set to 1 which always defers to the mutation rate.

To summarize, the probability represents the chance of mutation on the instance level and the rate represents the chance on the gene level. The probability and rate can be any number from 0 to 1. When the probability is 0, no mutation will ever happen. When the probability is not 0 but the rate is 0, then any instance that undergoes mutation will only receive one mutant gene. If the rate is not 0, then if an instance has been chosen to undergo mutation, each of its genes will mutate with a probability as defined by the rate.

Custom mutation objects must implement the #call method which accepts the population as the first object.

Examples:

Example Initializations:

Evolvable::Mutation.new # Approximately #{DEFAULT_PROBABILITY} of instances will receive one mutant gene
Evolvable::Mutation.new(probability: 0.5) # Approximately 50% of instances will receive one mutant gene
Evolvable::Mutation.new(rate: 0.03) # Approximately  3% of all genes in the population will mutate.
Evolvable::Mutation.new(probability: 0.3, rate: 0.03) # Approximately 30% of instances will have approximately 3% of their genes mutated.


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# File 'lib/evolvable/mutation.rb', line 57

def initialize(probability: nil, rate: nil)
  @probability = probability || (rate ? 1 : DEFAULT_PROBABILITY)
  @rate = rate
end

Instance Attribute Details

#probability ⇒ Object

Returns the value of attribute probability.



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# File 'lib/evolvable/mutation.rb', line 62

def probability
  @probability
end

#rate ⇒ Object

Returns the value of attribute rate.



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# File 'lib/evolvable/mutation.rb', line 62

def rate
  @rate
end

Instance Method Details

#call(population) ⇒ Object 



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# File 'lib/evolvable/mutation.rb', line 65

def call(population)
  mutate_evolvables(population.evolvables) unless probability.zero?
  population
end

#mutate_evolvables(evolvables) ⇒ Object 



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# File 'lib/evolvable/mutation.rb', line 70

def mutate_evolvables(evolvables)
  evolvables.each do |evolvable|
    next unless rand <= probability

    evolvable.genome.each { |_key, config| mutate_genes(config[:genes]) }
  end
end