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ec.vector.README Maven / Gradle / Ivy

This package, and the 'breed' subpackage contained inside, implement basic 
vector representations common in evolution
strategies and genetic algorithms.  The package is straightforward.  There
are various VectorIndividuals, each with an associated VectorSpecies that
it uses to maintain certain constraints (such as the minimum and maximum
gene values in the vector).

VectorIndividuals can be used with any breeding pipeline you care to design,
but since certain crossover and mutation methods are so common, the individuals
themselves implement those methods, and the VectorMutationPipeline and
VectorCrossoverPipeline are designed not to perform those methods but simply
to trigger the individuals into performing it themselves.  Thus if you
want to create a custom crossover procedure that's different from the
standard ones, you can do so simply by overriding the appropriate
defaultCrossover() method in the individual class, rather than making
a new pipeline.

VectorIndividuals also have significant numbers of hooks for variable-length
vector representations.

Note that there are different VectorIndividuals for different basic types.  For
example, there's a BitVectorIndividual and a FloatVectorIndividual, etc.
This doesn't use Java's generics facility.  Why?  Because Java's generics
are *extremely* slow.  They simplify the implementation of code like this but
at a very very high cost, and so ECJ just breaks out the individuals on a per-
type basis for efficiency purposes.

The various vector representations and their associated species and basic 
types are:

INDIVIDUAL			SPECIES			BASIC TYPE
BitVectorIndividual		BitVectorSpecies	boolean
ByteVectorIndividual		IntegerVectorSpecies	byte
ShortVectorIndividual		IntegerVectorSpecies	short
IntegerVectorIndividual		IntegerVectorSpecies	int
LongVectorIndividual		IntegerVectorSpecies	long
FloatVectorIndividual		FloatVectorSpecies	float
DoubleVectorIndividual		FloatVectorSpecies	double
GeneVectorIndividual		GeneVectorSpecies	Gene


Some items to note about certain species:


ec.vector.VectorSpecies

This is the superclass of all vector species, and defines three kinds of 
crossover: one-point, two-point, and uniform crossover (referred to as 'any'),
with a per-gene crossover probability for uniform crossover.  Additionally, 
a mutation probability specifies a per-gene likelihood of performing 
mutation on that gene (the kind of mutation depends on the particular 
vector individual being used).  And a per-gene number of retries to guarantee
different gene values under mutation is also provided.

VectorSpecies also allows you to specify a *chunk size*.  Chunks are regions
in which no crossover is allowed.  Crossover only occurs on chunk boundaries.
This allows you, for example, to indicate that an individual consists of
chunks 12 boolean values long (say), and that they are to be treated as atomic
units by the crossover operator -- it can't cross over within the chunk.


ec.vector.BitVectorSpecies

BitVectorSpecies is a VectorSpecies and has all of its feature.  Additionally
you can specify two kinds of mutation: bit-flip or reset.


ec.vector.FloatVectorSpecies

This class, like IntegerVectorSpecies, has all the features of VectorSpecies,
and furthermore has min and max gene values specified on a global, segment,
and per-gene basis.  

The default mutation procedure for FloatVectorSpecies can be either
randomization or adding gaussian random noise with a specified mutation
standard deviation.  If the random noise exceeds the min and max bounds
for that gene, FloatVectorSpecies will retry (you can specify how many
times) before giving up and not mutating the gene.


ec.vector.GeneVectorSpecies

This class is a VectorSpecies and so has all of its features.  However the
atomic type of the vector array isn't a number or boolean, but rather a 
specific object called a Gene; or more specifically, a subclass of
Gene which you specify (with the 'gene' parameter).  The objective
of this Species and GeneVectorIndividual is to enable you to have arbitrary
genes of any kind you like -- just stick your data in your Gene
subclass.




Other classes of importance:


ec.vector.Gene

This class is used with GeneVectorIndividual and GeneVectorSpecies to give you
flexibility with regard to the makeup of genes in the individual.  To implement
a Gene subclass, you'll need to provide a few basic methods (equality
testing, hash codes, the reset method, the mutation method) and optionally some
print facilities, depending on your needs.


ec.vector.breed.VectorMutationPipeline

Defines a basic mutation breeding pipeline for vector individuals.  The class
is very simple: when it is charged to produce a child, it requests a child
from its source, then calls defaultMutate() on that child and returns it.


ec.vector.breed.VectorCrossoverPipeline

Defines a basic crossover breeding pipeline for vector individuals.  The class
is very simple: when it is charged to produce children, it requests a child
from each of its sources, then calls defaultCrossover() on one child, passing
in the other child, to get them to cross over with one another. It then returns
the children.


ec.vector.breed.ListCrossoverPipeline	[UNTESTED]

Defines one-point and two-point crossover for vector individuals whose length may
vary.  This crossover pipeline may be useful for representations which are lists
rather than fixed-length vectors.


ec.vector.breed.MultiCrossoverPipeline	[UNTESTED]

Performs a version of N-person multiple crossover.  The size of N is determined
by the number of sources provided to the pipeline.  For each gene, the gene
values among the N indivdiuals are shuffled.  The resulting children are then
returned.