from pygenalgo.genome.chromosome import Chromosome
from pygenalgo.operators.mutation.mutate_operator import MutationOperator
[docs]
class InverseMutator(MutationOperator):
"""
Description:
Inverse mutator mutates the chromosome by inverting the order of
the gene values between two randomly selected gene end-positions.
"""
def __init__(self, mutate_probability: float = 0.1) -> None:
"""
Construct a 'InverseMutator' object with a given probability value.
:param mutate_probability: (float).
"""
# Call the super constructor with the provided probability value.
super().__init__(mutate_probability)
# _end_def_
[docs]
def mutate(self, individual: Chromosome) -> None:
"""
Perform the mutation operation by inverting the genes
between at two random positions.
:param individual: (Chromosome).
:return: None.
"""
# If the mutation probability is higher than
# a uniformly random value, make the changes.
if self.is_operator_applicable():
# Get the size of the chromosome.
n_genes: int = len(individual)
# Select randomly two mutation end-points.
i, j = self.rng.choice(n_genes, size=2, replace=False)
# Swap indices (if necessary).
if i > j:
i, j = j, i
# _end_if_
# Make a slice list of the genes
# we want to inverse their order: i -> j.
sliced_chromosome = individual.genome[i:j]
# Invert the copied slice in place.
sliced_chromosome.reverse()
# Put back the inverse items.
individual.genome[i:j] = sliced_chromosome
# Set the fitness to NaN.
individual.invalidate_fitness()
# Increase the mutator counter.
self.inc_counter()
# _end_def_
# _end_class_