ec.gp.koza

Class HalfBuilder

java.lang.Object

ec.gp.GPNodeBuilder

ec.gp.koza.KozaBuilder

ec.gp.koza.HalfBuilder

All Implemented Interfaces:

Prototype, Setup, Serializable, Cloneable

public class HalfBuilder
extends KozaBuilder

HalfBuilder is a GPNodeBuilder which implements the RAMPED HALF-AND-HALF tree building method described in Koza I/II.

RAMPED HALF-AND-HALF works by choosing a random integer d between minDepth and maxDepth, inclusive. It then grows a tree of depth 1 to d inclusive. (1-pickGrowProbability) of the time (by default, 0.5) it grows a tree using the FULL method, which generates full trees of exactly depth d. (pickGrowProbability) of the time, it grows a tree using the GROW method, which may generate trees of any size between 1 and d inclusive.

Actually, claiming to implement the Koza I/II approach is a bit of a fib -- Koza's original code is somewhat ad-hoc. In the Koza approach, d is chosen in a kind of round-robin fashion rather than at random, if RAMPED HALF/HALF is used. Also, for all three algorithms (RAMPED HALF/HALF, GROW, FULL), the algorithm will not generate a tree consisting of a single terminal, unless forced to.

This implementation instead follows lil-gp's approach, which is to choose d at random from between minDepth and maxDepth, inclusive, and to allow trees consisting of single terminals.

Determining what various algorithms do is a little confusing, mostly because the source code for lil-gp and Koza don't actually quite do what they claim. The table below lists the depth values actually used (counting nodes, rather than edges, for depth). It's probably not what you had expected!

	Koza I Min	Koza I Max	Koza II Min	Koza II Max	lil-gp Min	lil-gp Max	ECJ Min	ECJ Max
GROW (mut)	5	5	5	5			5	5
GROW (new)	7	7	6? 7?	6? 7?	3	7	5	5
FULL (new)	7	7	6? 7?	6? 7?	3	7
HALF (new)	2	6	2	5? 6?	3	7	2	6

The table cell is empty when that parameter is not defined by the system by default. Koza II has two values each because of a possible typo in the text -- while page 656 gives one maximum, page 671 gives another. Note the odd fact that in Koza I/II GROW and FULL have effectively one-deeper tree values than HALF does, even though they use the same code parameters! This is because of a quirk in Koza's code.

This algorithm ignores requestedSize, so no pipelines can ask it to grow a tree of a specific fixed size. The algorithm also ignores any user-provided size distributions.

Parameters

base.growp 0.0 <= double <= 1.0	(the likelihood of choosing GROW (as opposed to FULL)>
base.min-depth int >= 1	(smallest "maximum" depth the builder may use for building a tree. 2 is the default.)
base.max-depth int >= base.min-depth	(largest "maximum" depth the builder may use for building a tree. 6 is the default.)

Default Base
gp.koza.half

Version:

1.0

Author:

Sean Luke

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
static String	P_HALFBUILDER
static String	P_PICKGROWPROBABILITY
double	pickGrowProbability The likelihood of using GROW over FULL.

Fields inherited from class ec.gp.koza.KozaBuilder

maxDepth, minDepth, P_MAXDEPTH, P_MINDEPTH

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
HalfBuilder()

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)
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.koza.KozaBuilder

fullNode, growNode

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_HALFBUILDER

public static final String P_HALFBUILDER

See Also:

Constant Field Values

P_PICKGROWPROBABILITY

public static final String P_PICKGROWPROBABILITY

See Also:

Constant Field Values

pickGrowProbability

public double pickGrowProbability

The likelihood of using GROW over FULL.

Constructor Detail

HalfBuilder

public HalfBuilder()

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 KozaBuilder

newRootedTree

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

Specified by:

newRootedTree in class GPNodeBuilder