public class HalfBuilder extends KozaBuilder
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 |
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
Modifier and Type | Field and Description |
---|---|
static java.lang.String |
P_HALFBUILDER |
static java.lang.String |
P_PICKGROWPROBABILITY |
double |
pickGrowProbability
The likelihood of using GROW over FULL.
|
maxDepth, minDepth, P_MAXDEPTH, P_MINDEPTH
CHECK_BOUNDARY, maxSize, minSize, NOSIZEGIVEN, P_MAXSIZE, P_MINSIZE, P_NUMSIZES, P_SIZE, sizeDistribution
Constructor and Description |
---|
HalfBuilder() |
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.
|
fullNode, growNode
canPick, clone, errorAboutNoNodeWithType, pickSize, warnAboutNonterminal, warnAboutNonTerminalWithType, warnAboutNoTerminalWithType
public static final java.lang.String P_HALFBUILDER
public static final java.lang.String P_PICKGROWPROBABILITY
public double pickGrowProbability
public Parameter defaultBase()
Prototype
public void setup(EvolutionState state, Parameter base)
Prototype
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.
public GPNode newRootedTree(EvolutionState state, GPType type, int thread, GPNodeParent parent, GPFunctionSet set, int argposition, int requestedSize)
newRootedTree
in class GPNodeBuilder