individuals.rst

Individuals

This section covers the class Individual in more detail.

Class Summary

Figure 1: The `Individual` class This class diagram shows the detail for Individual. In additional to the association with Decoder and ProbLem, each Individual has a genome and fitness. There are also several member functions for cloning, decoding, and evaluating individuals. Not shown are such member functions as __repr__() and __str__().

An Individual poses a unique instance of a solution to the associated Problem. Each Individual has a genome, which contains state representing that posed solution. The genome can be a sequence or a matrix or a tree or some other data structure, but in practice a genome is usually a binary or a real-value sequence. Every Individual is connected to an associated Problem and relies on the Problem to evaluate its fitness and to compare itself with another Individual to determine the better of the two.

The clone() method will create a duplicate of a given Individual; the new Individual gets a deep copy of the genome and refers to the same Problem and Decoder. evaluate() calls evaluate_imp()`that, in turn, calls `decode()`to translate the `genome into phenomes, or values meaningful to the Problem, and then passes those values to the Problem where it returns a fitness. This fitness is then assigned to the Individual.

The reason for the indirection using evaluate_imp() is that evaluate_imp() allows sub-classes to pass ancillary information to Problem during evaluation. For example, an Individual may have a UUID that the Problem needs in order to create a file or sub-directory using that UUID. evaluate_imp() can be over-ridden in a sub-class to pass along the UUID in addition to the decoded genome.

The @total_ordering class wrapper is used to expand the member functions __lt__() and __eq__() that are, in turn, heavily used in sorting, selection, and comparison operators.

RobustIndividual

RobustIndividual is a sub-class of Individual that over-rides evaluate() to handle exceptions thrown during evaluation. If no exceptions are thrown, then self.is_viable is set to True. If an exception happens, then the following occurs:

• self.is_viable is set to False
• self.fitness is set to math.nan
• self.exception is assigned the Exception object

In turn, this class has another sub-class leap_ec.distributed.individual.DistributedIndividual.

Class API

leap_ec.individual.RobustIndividual

leap_ec.individual.Individual

__init__

leap_ec.individual.RobustIndividual

__init__