io.jenetics.prog.regression

Interface Complexity<T>

Type Parameters:

T - the sample type

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.

@FunctionalInterface
public interface Complexity<T>

Represents a complexity measure if a given program tree. The program complexity ensures, that simpler programs with similar loss function values are preferred. It is part of the overall Error function.

final Error<Double> error = Error.of(LossFunction::mse, Complexity.ofMaxNodeCount(50));

Since:

5.0

Version:

5.0

Author:

Franz Wilhelmstötter

See Also:

LossFunction, Error

Method Summary

Modifier and Type	Method and Description
double	apply(Tree<? extends Op<T>,?> program) Calculates the complexity of the current program (possibly) relative to the actual error value.
static double	count(Tree<?,?> program, int maxNodes) This method uses the node count of a program tree for calculating its complexity.
static <T> Complexity<T>	ofNodeCount(int maxNodeCount) Return a complexity measure which counts the number of nodes of a program.

Method Detail

apply

double apply(Tree<? extends Op<T>,?> program)

Calculates the complexity of the current program (possibly) relative to the actual error value.

Parameters:

program - the actual program

Returns:

the measure of the program complexity

ofNodeCount

static <T> Complexity<T> ofNodeCount(int maxNodeCount)

Return a complexity measure which counts the number of nodes of a program.

Type Parameters:

T - the sample type

Parameters:

maxNodeCount - the maximal node count. The returned complexity will be one if the program node count is greater or equal the given count

Returns:

a program node count complexity measure

Throws:

IllegalArgumentException - if the max node count is smaller than one

See Also:

count(Tree, int)

count

static double count(Tree<?,?> program,
                    int maxNodes)

This method uses the node count of a program tree for calculating its complexity. The returned node count measure is within the range of [0, 1]. If the program contains only one node, zero is returned. If the node count is bigger or equal maxNodes, one is returned.

The complexity is calculated in the following way:

final double cc = min(program.size() - 1, maxNodes); return 1.0 - sqrt(1.0 - (cc*cc)/(maxNodes*maxNodes));

Parameters:

program - the program used for the complexity measure

maxNodes - the maximal expected node count

Returns:

the complexity measure of the given program

Throws:

NullPointerException - if the given program is null

IllegalArgumentException - if maxNodes is smaller than one

See Also:

ofNodeCount(int)