ec

Class Individual

java.lang.Object

ec.Individual

All Implemented Interfaces:

Prototype, Setup, Serializable, Cloneable, Comparable

Direct Known Subclasses:

ConstructiveIndividual, GPIndividual, RuleIndividual, VectorIndividual

public abstract class Individual
extends Object
implements Prototype, Comparable

An Individual is an item in the EC population stew which is evaluated and assigned a fitness which determines its likelihood of selection. Individuals are created most commonly by the newIndividual(...) method of the ec.Species class.

In general Individuals are immutable. That is, once they are created their genetic material should not be modified. This protocol helps insure that they are safe to read under multithreaded conditions. You can violate this protocol, but try to do so when you know you have only have a single thread.

In addition to serialization for checkpointing, Individuals may read and write themselves to streams in three ways.

• writeIndividual(...,DataOutput)/readIndividual(...,DataInput) This method transmits or receives an individual in binary. It is the most efficient approach to sending individuals over networks, etc. These methods write the evaluated flag and the fitness, then call readGenotype/writeGenotype, which you must implement to write those parts of your Individual special to your functions-- the default versions of readGenotype/writeGenotype throw errors. You don't need to implement them if you don't plan on using read/writeIndividual.
• printIndividual(...,PrintWriter)/readIndividual(...,LineNumberReader) This approach transmits or receives an indivdual in text encoded such that the individual is largely readable by humans but can be read back in 100% by ECJ as well. To do this, these methods will encode numbers using the ec.util.Code class. These methods are mostly used to write out populations to files for inspection, slight modification, then reading back in later on. readIndividualreads in the fitness and the evaluation flag, then calls parseGenotype to read in the remaining individual. You are responsible for implementing parseGenotype: the Code class is there to help you. printIndividual writes out the fitness and evaluation flag, then calls genotypeToString and printlns the resultant string. You are responsible for implementing the genotypeToString method in such a way that parseGenotype can read back in the individual println'd with genotypeToString. The default form of genotypeToString simply calls toString, which you may override instead if you like. The default form of parseGenotype throws an error. You are not required to implement these methods, but without them you will not be able to write individuals to files in a simultaneously computer- and human-readable fashion.
• printIndividualForHumans(...,PrintWriter) This approach prints an individual in a fashion intended for human consumption only. printIndividualForHumans writes out the fitness and evaluation flag, then calls genotypeToStringForHumans and printlns the resultant string. You are responsible for implementing the genotypeToStringForHumans method. The default form of genotypeToStringForHumans simply calls toString, which you may override instead if you like (though note that genotypeToString's default also calls toString). You should handle one of these methods properly to ensure individuals can be printed by ECJ.

Since individuals should be largely immutable, why is there a readIndividual method? after all this method doesn't create a new individual -- it just erases the existing one. This is largely historical; but the method is used underneath by the various newIndividual methods in Species, which do create new individuals read from files. If you're trying to create a brand new individual read from a file, look in Species.

Individuals are Comparable: if you sort Individuals, the FITTER individuals will appear EARLIER in a list or array.

Version:

1.0

Author:

Sean Luke

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
boolean	evaluated Has the individual been evaluated and its fitness determined yet?
static String	EVALUATED_PREAMBLE A string appropriate to put in front of whether or not the individual has been printed.
Fitness	fitness The fitness of the Individual.
static String	P_INDIVIDUAL A reasonable parameter base element for individuals
Species	species The species of the Individual.

Constructor Summary

Constructors

Constructor and Description
Individual()

Method Summary

Modifier and Type	Method and Description
Object	clone() Creates a new individual cloned from a prototype, and suitable to begin use in its own evolutionary context.
int	compareTo(Object o) Returns -1 if I am BETTER in some way than the other Individual, 1 if the other Individual is BETTER than me, and 0 if we are equivalent.
double	distanceTo(Individual otherInd) Returns the metric distance to another individual, if such a thing can be measured.
abstract boolean	equals(Object ind) Returns true if I am genetically "equal" to ind.
String	genotypeToString() Print to a string the genotype of the Individual in a fashion intended to be parsed in again via parseGenotype(...).
String	genotypeToStringForHumans() Print to a string the genotype of the Individual in a fashion readable by humans, and not intended to be parsed in again.
abstract int	hashCode() Returns a hashcode for the individual, such that individuals which are equals(...) each other always return the same hash code.
void	merge(EvolutionState state, Individual other) Replaces myself with the other Individual, while merging our evaluation results together.
protected void	parseGenotype(EvolutionState state, LineNumberReader reader) This method is used only by the default version of readIndividual(state,reader), and it is intended to be overridden to parse in that part of the individual that was outputted in the genotypeToString() method.
void	printIndividual(EvolutionState state, int log) Should print the individual in a way that can be read by computer, including its fitness, with a verbosity of Output.V_NO_GENERAL.
void	printIndividual(EvolutionState state, int log, int verbosity) Deprecated. Verbosity no longer used.
void	printIndividual(EvolutionState state, PrintWriter writer) Should print the individual in a way that can be read by computer, including its fitness.
void	printIndividualForHumans(EvolutionState state, int log) Should print the individual out in a pleasing way for humans, with a verbosity of Output.V_NO_GENERAL.
void	printIndividualForHumans(EvolutionState state, int log, int verbosity) Deprecated. Verbosity no longer used.
void	readGenotype(EvolutionState state, DataInput dataInput) Reads in the genotypic information from a DataInput, erasing the previous genotype of this Individual.
void	readIndividual(EvolutionState state, DataInput dataInput) Reads the binary form of an individual from a DataInput, erasing the previous information stored in this Individual.
void	readIndividual(EvolutionState state, LineNumberReader reader) Reads in the individual from a form printed by printIndividual(), erasing the previous information stored in this Individual.
void	setup(EvolutionState state, Parameter base) This should be used to set up only those things which you share in common with all other individuals in your species; individual-specific items which make you you should be filled in by Species.newIndividual(...), and modified by breeders.
long	size() Returns the "size" of the individual.
String	toString() Overridden here because hashCode() is not expected to return the pointer to the object.
void	writeGenotype(EvolutionState state, DataOutput dataOutput) Writes the genotypic information to a DataOutput.
void	writeIndividual(EvolutionState state, DataOutput dataOutput) Writes the binary form of an individual out to a DataOutput.

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface ec.Prototype

defaultBase

Field Detail

P_INDIVIDUAL

public static final String P_INDIVIDUAL

A reasonable parameter base element for individuals

See Also:

Constant Field Values

EVALUATED_PREAMBLE

public static final String EVALUATED_PREAMBLE

A string appropriate to put in front of whether or not the individual has been printed.

See Also:

Constant Field Values

fitness

public Fitness fitness

The fitness of the Individual.

species

public Species species

The species of the Individual.

evaluated

public boolean evaluated

Has the individual been evaluated and its fitness determined yet?

Constructor Detail

Individual

public Individual()

Method Detail

clone

public Object clone()

Description copied from interface: Prototype

Creates a new individual cloned from a prototype, and suitable to begin use in its own evolutionary context.

Typically this should be a full "deep" clone. However, you may share certain elements with other objects rather than clone hem, depending on the situation:

• If you hold objects which are shared with other instances, don't clone them.
• If you hold objects which must be unique, clone them.
• If you hold objects which were given to you as a gesture of kindness, and aren't owned by you, you probably shouldn't clone them.
• DON'T attempt to clone: Singletons, Cliques, or Populations, or Subpopulation.
• Arrays are not cloned automatically; you may need to clone an array if you're not sharing it with other instances. Arrays have the nice feature of being copyable by calling clone() on them.

Implementations.

• If no ancestor of yours implements clone(), and you have no need to do clone deeply, and you are abstract, then you should not declare clone().
• If no ancestor of yours implements clone(), and you have no need to do clone deeply, and you are not abstract, then you should implement it as follows:

   public Object clone() 
       {
       try
           { 
           return super.clone();
           }
       catch ((CloneNotSupportedException e)
           { throw new InternalError(); } // never happens
       }
          

• If no ancestor of yours implements clone(), but you need to deep-clone some things, then you should implement it as follows:

   public Object clone() 
       {
       try
           { 
           MyObject myobj = (MyObject) (super.clone());
  
           // put your deep-cloning code here...
           }
       catch ((CloneNotSupportedException e)
           { throw new InternalError(); } // never happens
       return myobj;
       } 
          

• If an ancestor has implemented clone(), and you also need to deep clone some things, then you should implement it as follows:

   public Object clone() 
       { 
       MyObject myobj = (MyObject) (super.clone());
  
       // put your deep-cloning code here...
  
       return myobj;
       } 
          

Specified by:

clone in interface Prototype

Overrides:

clone in class Object

size

public long size()

Returns the "size" of the individual. This is used for things like parsimony pressure. The default form of this method returns 0 -- if you care about parsimony pressure, you'll need to override the default to provide a more descriptive measure of size.

equals

public abstract boolean equals(Object ind)

Returns true if I am genetically "equal" to ind. This should mostly be interpreted as saying that we are of the same class and that we hold the same data. It should NOT be a pointer comparison.

Overrides:

equals in class Object

hashCode

public abstract int hashCode()

Returns a hashcode for the individual, such that individuals which are equals(...) each other always return the same hash code.

Overrides:

hashCode in class Object

toString

public String toString()

Overridden here because hashCode() is not expected to return the pointer to the object. toString() normally uses hashCode() to print a unique identifier, and that's no longer the case. You're welcome to override this anyway you like to make the individual print out in a more lucid fashion.

Overrides:

toString in class Object

genotypeToStringForHumans

public String genotypeToStringForHumans()

Print to a string the genotype of the Individual in a fashion readable by humans, and not intended to be parsed in again. The fitness and evaluated flag should not be included. The default form simply calls toString(), but you'll probably want to override this to something else.

genotypeToString

public String genotypeToString()

Print to a string the genotype of the Individual in a fashion intended to be parsed in again via parseGenotype(...). The fitness and evaluated flag should not be included. The default form simply calls toString(), which is almost certainly wrong, and you'll probably want to override this to something else.

setup

public void setup(EvolutionState state,
                  Parameter base)

This should be used to set up only those things which you share in common with all other individuals in your species; individual-specific items which make you you should be filled in by Species.newIndividual(...), and modified by breeders.

Specified by:

setup in interface Prototype

Specified by:

setup in interface Setup

See Also:

Prototype.setup(EvolutionState,Parameter)

printIndividualForHumans

public void printIndividualForHumans(EvolutionState state,
                                     int log)

Should print the individual out in a pleasing way for humans, with a verbosity of Output.V_NO_GENERAL.

printIndividualForHumans

public final void printIndividualForHumans(EvolutionState state,
                                           int log,
                                           int verbosity)

Deprecated. Verbosity no longer used.

Should print the individual out in a pleasing way for humans, including its fitness, using state.output.println(...,verbosity,log) You can get fitness to print itself at the appropriate time by calling fitness.printFitnessForHumans(state,log,verbosity);

The default form of this method simply prints out whether or not the individual has been evaluated, its fitness, and then calls Individual.genotypeToStringForHumans(). Feel free to override this to produce more sophisticated behavior, though it is rare to need to -- instead you could just override genotypeToStringForHumans().

printIndividual

public void printIndividual(EvolutionState state,
                            int log)

Should print the individual in a way that can be read by computer, including its fitness, with a verbosity of Output.V_NO_GENERAL.

printIndividual

public final void printIndividual(EvolutionState state,
                                  int log,
                                  int verbosity)

Deprecated. Verbosity no longer used.

Should print the individual in a way that can be read by computer, including its fitness, using state.output.println(...,verbosity,log) You can get fitness to print itself at the appropriate time by calling fitness.printFitness(state,log,verbosity);

The default form of this method simply prints out whether or not the individual has been evaluated, its fitness, and then calls Individual.genotypeToString(). Feel free to override this to produce more sophisticated behavior, though it is rare to need to -- instead you could just override genotypeToString().

printIndividual

public void printIndividual(EvolutionState state,
                            PrintWriter writer)

Should print the individual in a way that can be read by computer, including its fitness. You can get fitness to print itself at the appropriate time by calling fitness.printFitness(state,log,writer); Usually you should try to use printIndividual(state,log,verbosity) instead -- use this method only if you can't print through the Output facility for some reason.

The default form of this method simply prints out whether or not the individual has been evaluated, its fitness, and then calls Individual.genotypeToString(). Feel free to override this to produce more sophisticated behavior, though it is rare to need to -- instead you could just override genotypeToString().

readIndividual

public void readIndividual(EvolutionState state,
                           LineNumberReader reader)
                    throws IOException

Reads in the individual from a form printed by printIndividual(), erasing the previous information stored in this Individual. If you are trying to create an Individual from information read in from a stream or DataInput, see the various newIndividual() methods in Species. The default form of this method simply reads in evaluation information, then fitness information, and then calls parseGenotype() (which you should implement). The Species is not changed or attached, so you may need to do that elsewhere. Feel free to override this method to produce more sophisticated behavior, though it is rare to need to -- instead you could just override parseGenotype().

Throws:

IOException

parseGenotype

protected void parseGenotype(EvolutionState state,
                             LineNumberReader reader)
                      throws IOException

This method is used only by the default version of readIndividual(state,reader), and it is intended to be overridden to parse in that part of the individual that was outputted in the genotypeToString() method. The default version of this method exits the program with an "unimplemented" error. You'll want to override this method, or to override readIndividual(...) to not use this method.

Throws:

IOException

writeIndividual

public void writeIndividual(EvolutionState state,
                            DataOutput dataOutput)
                     throws IOException

Writes the binary form of an individual out to a DataOutput. This is not for serialization: the object should only write out the data relevant to the object sufficient to rebuild it from a DataInput. The Species will be reattached later, and you should not write it. The default version of this method writes the evaluated and fitness information, then calls writeGenotype() to write the genotype information. Feel free to override this method to produce more sophisticated behavior, though it is rare to need to -- instead you could just override writeGenotype().

Throws:

IOException

writeGenotype

public void writeGenotype(EvolutionState state,
                          DataOutput dataOutput)
                   throws IOException

Writes the genotypic information to a DataOutput. Largely called by writeIndividual(), and nothing else. The default simply throws an error. Various subclasses of Individual override this as appropriate. For example, if your custom individual's genotype consists of an array of integers, you might do this:

 dataOutput.writeInt(integers.length);
 for(int x=0;x

Throws:

IOException

readGenotype

public void readGenotype(EvolutionState state,
                         DataInput dataInput)
                  throws IOException

Reads in the genotypic information from a DataInput, erasing the previous genotype of this Individual. Largely called by readIndividual(), and nothing else. If you are trying to create an Individual from information read in from a stream or DataInput, see the various newIndividual() methods in Species. The default simply throws an error. Various subclasses of Individual override this as appropriate. For example, if your custom individual's genotype consists of an array of integers, you might do this:

 integers = new int[dataInput.readInt()];
 for(int x=0;x

Throws:

IOException

readIndividual

public void readIndividual(EvolutionState state,
                           DataInput dataInput)
                    throws IOException

Reads the binary form of an individual from a DataInput, erasing the previous information stored in this Individual. This is not for serialization: the object should only read in the data written out via printIndividual(state,dataInput). If you are trying to create an Individual from information read in from a stream or DataInput, see the various newIndividual() methods in Species. The default form of this method simply reads in evaluation information, then fitness information, and then calls readGenotype() (which you will need to override -- its default form simply throws an error). The Species is not changed or attached, so you may need to do that elsewhere. Feel free to override this method to produce more sophisticated behavior, though it is rare to need to -- instead you could just override readGenotype().

Throws:

IOException

distanceTo

public double distanceTo(Individual otherInd)

Returns the metric distance to another individual, if such a thing can be measured. Subclassess of Individual should implement this if it exists for their representation. The default implementation here, which isn't very helpful, returns 0 if the individuals are equal and infinity if they are not.

compareTo

public int compareTo(Object o)

Returns -1 if I am BETTER in some way than the other Individual, 1 if the other Individual is BETTER than me, and 0 if we are equivalent. The default implementation assumes BETTER means FITTER, by simply calling compareTo on the fitnesses themse.ves

Specified by:

compareTo in interface Comparable

merge

public void merge(EvolutionState state,
                  Individual other)

Replaces myself with the other Individual, while merging our evaluation results together. May destroy the other Individual in the process. By default this procedure calls fitness(merge) to merge the old fitness (backwards) into the new fitness, then entirely overwrites myself with the other Individual (including the merged fitness).

What is the purpose of this method? When coevolution is done in combination with distributed evaluation, an Individual may be sent to multiple remote sites to be tested in different trials prior to having a completed fitness assessed. As those trials complete, we need a way to merge them together. By default this method simply merges the trial arrays (using fitness.merge(...)), and determines the "best" context, then copies the other Individual to me. But if you store additional trial results outside fitness---for example, if you keep around the best collaborators from coevolution, say---you may need a way to guarantee that this Individual reflects the most up to date information about recent trials arriving via the other Individual. In this case, override the method and perform merging by hand.