ec.gp.build

Class PTC1

java.lang.Object

ec.gp.GPNodeBuilder

ec.gp.build.PTC1

All Implemented Interfaces:

Prototype, Setup, Serializable, Cloneable

public class PTC1
extends GPNodeBuilder

PTC1 implements the "Strongly-typed Probabilistic Tree Creation 1 (PTC1)" algorithm described in

Luke, Sean. 2000. Issues in Scaling Genetic Programming: Breeding Strategies, Tree Generation, and Code Bloat. Ph.D. Dissertation, Department of Computer Science, University of Maryland, College Park, Maryland.

...and also in

Luke, Sean. 2000. Two fast tree-creation algorithms for genetic programming. In IEEE Transactions on Evolutionary Computation 4:3 (September 2000), 274-283. IEEE.

Both can be found at http://www.cs.gmu.edu/~sean/papers/

PTC1 requires that your function set to implement PTCFunctionSetForm. The provided function set, PTCFunctionSet, does exactly this.

The Strongly-typed PTC1 algorithm is a derivative of the GROW algorithm used in ec.gp.koza.GrowBuilder. The primary differences are:

• PTC1 guarantees that trees generated will have an expected (mean) tree size, provided by the user. There is no guarantee on variance. This is different from GROW, which doesn't give any user control at all.
• PTC1 does not have a min-depth value. In essence, PTC1's min-depth value is always set to 1.
• PTC1's max-depth value should really only be used to enforce a large memory restriction. Unlike GROW, where it's used to keep GROW from going nuts.
• PTC1 has provisions for picking nonterminals with various probabilities over other nonterminals (and likewise for terminals). To use this, tweak the PTCFunctionSetForm object.

PTC1 assumes that the requested size passed to newRootedTree(...) is the expected size. If the value is NOSIZEGIVEN, then PTC1 will use the expected size defined by the expected-size parameter.

Parameters

base.expected-size int >= 1	default expected tree size
base.max-depth int >= 1	maximum allowable tree depth (usually a big value)

Default Base
gp.build.ptc1

Version:

1.0

Author:

Sean Luke

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
int	expectedSize The default expected tree size for PTC1
int	maxDepth The largest maximum tree depth PTC1 can specify -- should be big.
static String	P_EXPECTED
static String	P_MAXDEPTH
static String	P_PTC1

Fields inherited from class ec.gp.GPNodeBuilder

CHECK_BOUNDARY, maxSize, minSize, NOSIZEGIVEN, P_MAXSIZE, P_MINSIZE, P_NUMSIZES, P_SIZE, sizeDistribution

Constructor Summary

Constructors

Constructor and Description
PTC1()

Method Summary

Methods

Modifier and Type	Method and Description
Parameter	defaultBase() Returns the default base for this prototype.
GPNode	newRootedTree(EvolutionState state, GPType type, int thread, GPNodeParent parent, GPFunctionSet set, int argposition, int requestedSize)
private GPNode	ptc1(EvolutionState state, int current, GPType type, int thread, GPNodeParent parent, int argposition, GPFunctionSet set, PTCFunctionSetForm pset, double[] nonterminalSelectionProbabilities) A private function which recursively returns a GROW tree to newRootedTree(...)
void	setup(EvolutionState state, Parameter base) Sets up the object by reading it from the parameters stored in state, built off of the parameter base base.

Methods inherited from class ec.gp.GPNodeBuilder

canPick, clone, errorAboutNoNodeWithType, pickSize, warnAboutNonterminal, warnAboutNonTerminalWithType, warnAboutNoTerminalWithType

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

P_PTC1

public static final String P_PTC1

See Also:

Constant Field Values

P_EXPECTED

public static final String P_EXPECTED

See Also:

Constant Field Values

P_MAXDEPTH

public static final String P_MAXDEPTH

See Also:

Constant Field Values

maxDepth

public int maxDepth

The largest maximum tree depth PTC1 can specify -- should be big.

expectedSize

public int expectedSize

The default expected tree size for PTC1

Constructor Detail

PTC1

public PTC1()

Method Detail

defaultBase

public Parameter defaultBase()

Description copied from interface: Prototype

Returns the default base for this prototype. This should generally be implemented by building off of the static base() method on the DefaultsForm object for the prototype's package. This should be callable during setup(...).

setup

public void setup(EvolutionState state,
         Parameter base)

Description copied from interface: Prototype

Sets up the object by reading it from the parameters stored in state, built off of the parameter base base. If an ancestor implements this method, be sure to call super.setup(state,base); before you do anything else.

For prototypes, setup(...) is typically called once for the prototype instance; cloned instances do not receive the setup(...) call. setup(...) may be called more than once; the only guarantee is that it will get called at least once on an instance or some "parent" object from which it was ultimately cloned.

Specified by:

setup in interface Prototype

Specified by:

setup in interface Setup

Overrides:

setup in class GPNodeBuilder

newRootedTree

public GPNode newRootedTree(EvolutionState state,
                   GPType type,
                   int thread,
                   GPNodeParent parent,
                   GPFunctionSet set,
                   int argposition,
                   int requestedSize)

Specified by:

newRootedTree in class GPNodeBuilder

ptc1

private GPNode ptc1(EvolutionState state,
          int current,
          GPType type,
          int thread,
          GPNodeParent parent,
          int argposition,
          GPFunctionSet set,
          PTCFunctionSetForm pset,
          double[] nonterminalSelectionProbabilities)

A private function which recursively returns a GROW tree to newRootedTree(...)