MUTATION

Mutation documentation

A mutation operator mutates a single instance in place.

The mutation operator should be defined as a mutate! method in your genotype class.

   class Example < Genotype
     def mutate!
       # apply mutation here.
     end
     use NullMutator # or include some builtin operator
   end

The non-destructive counterpart mutate is defined automatically by Genotype#mutate.

General Mutators

NullMutator

Just returns self

List-based Mutators

These mutators can be used for all list- and string-based genotypes.

ListMutator(strategy=:expected_n ,point_mutator=:uniform)

Generates a wide variety of mutators for lists, strings and bitstrings.

• strategy can be a proc or one of the MutationStrategies : single point, multi-point and probabilistic.
• point_mutator can be a proc or one of the PointMutators : bit flipping, replacing elements, or adding some offset.

See the documentation of list_mutate.rb for more info on these.

Both of these parameters use Symbol#[] in the examples. :replace[‘a’,’b’] is simply equivalent to [:replace,’a’,’b’]

Matrix-based Mutators

These mutators can be used for all matrix genotypes.

MatrixMutator(strategy=:expected_n ,point_mutator=:uniform)

Generates a wide variety of mutators for matrices of floats or bits.

• strategy can be a proc or one of the MatrixMutationStrategies : single point, multi-point and probabilistic. See the documentation of matrix.rb for more info on these.
• point_mutator can be a proc or one of the PointMutators, as with ListMutator.

Specialized Mutators

For PermutationGenotype

All of these will probably work on other array/string/matrix-based genotypes as well, but this is untested.

• TranspositionMutator is a transposition mutator for permutations. It interchanges two elements and leaves the remaining elements in their original positions.
• InversionMutator is another mutator for permutations. It inverses a part of the genes array.
• InsertionMutator takes a random element of the permutation, and inserts it at a random position.
• RotationMutator takes a random element, and rotates the permutation such that this is the first element, i.e. it effectively does nothing if the permutation represents a cycle.

For TreeGenotype ->file

• TreeReplaceMutator(depth,type) replaces a randomly chosen subtree with a new, randomly generated, subtree.
• TreePruneMutator replaces a randomly chosen subtree with a randomly generated terminal.
• TreeRemoveNodeMutator replaces a random node by one of its children.
• TreeChopMutator replaces the root by one of its children.
• TreeInsertNodeMutator replaces a random node x by a new operator node having x as one of its children.
• TreeTerminalMutator replaces a random terminal by a new one.
• TreeNumTerminalMutator(mutate=:uniform[ 0.1 ]) mutates a random numeric terminal.
• TreeEvalMutator(values_hash=Hash{0}) replaces a random terminal by the result of its evaluation.

Meta-mutators

These functions take one or more mutator modules and generate a new mutator module.

PMutate(p,mutator,othermutator=NullMutator)

Applies an arbitrary mutator with probability p, and another mutator with probability 1-p.

PMutateN(hash of module=>probability pairs)

Version of PMutate for more than two mutators. If sum(probability) < 1, NullMutator will be used for the remaining probability.