net.sf.tweety.logics.pl.util

Class SyntacticRandomPlBeliefSetSampler

java.lang.Object

net.sf.tweety.commons.BeliefBaseSampler<PlBeliefSet>

net.sf.tweety.logics.pl.util.SyntacticRandomPlBeliefSetSampler

public class SyntacticRandomPlBeliefSetSampler
extends net.sf.tweety.commons.BeliefBaseSampler<PlBeliefSet>

This sampler implements a random generation algorithm for generating formulas, based on the syntax tree of propositional formulas. Consider the following BNF for a propositional logic formula:

F ::== !F | F && F | F || F | A

with propositions A. The algorithm for constructing formulas takes four parameters:

• probneg: the probability to generate a negation
• probconj: the probability to generate a conjunction
• probdisj: the probability to generate a disjunction
• recDecrease: a value in (0,1) by which the above probabilities are multiplied in each recursive step to increase likelihood of termination.

From these parameters the probability to generate a proposition "probprop" is computed via probprop=1-probneg-probconj-probdisj (the actual proposition is selected with a uniform distribution). Then a formula is generated by randomly selecting which rule in the above BNF is followed wrt. these probabilities. Note that the algorithm is not guaranteed to terminate.

Author:

Matthias Thimm

Field Summary

Fields inherited from class net.sf.tweety.commons.BeliefBaseSampler

DEFAULT_MAXIMUM_BELIEFBASE_LENGTH, DEFAULT_MINIMUM_BELIEFBASE_LENGTH

Constructor Summary

Constructors

Constructor and Description
SyntacticRandomPlBeliefSetSampler(net.sf.tweety.commons.Signature signature, net.sf.tweety.math.probability.Probability probneg, net.sf.tweety.math.probability.Probability probconj, net.sf.tweety.math.probability.Probability probdisj, double recDecrease) Creates a new sampler.

Method Summary

Modifier and Type	Method and Description
PlBeliefSet	randomSample(int minLength, int maxLength)
PropositionalFormula	sampleFormula(net.sf.tweety.math.probability.ProbabilityFunction<Byte> prob) Samples a single formula.

Methods inherited from class net.sf.tweety.commons.BeliefBaseSampler

getSignature, randomSample, randomSample

Methods inherited from class java.lang.Object

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

Constructor Detail

SyntacticRandomPlBeliefSetSampler

public SyntacticRandomPlBeliefSetSampler(net.sf.tweety.commons.Signature signature,
                                         net.sf.tweety.math.probability.Probability probneg,
                                         net.sf.tweety.math.probability.Probability probconj,
                                         net.sf.tweety.math.probability.Probability probdisj,
                                         double recDecrease)

Creates a new sampler.

Parameters:

signature - some set of propositions

probneg - the probability to generate a negation

probconj - the probability to generate a conjunction

probdisj - the probability to generate a disjunction

recDecrease - a value in (0,1) by which the above probabilities are multiplied in each recursive step to increase likelihood of termination.

Method Detail

sampleFormula

public PropositionalFormula sampleFormula(net.sf.tweety.math.probability.ProbabilityFunction<Byte> prob)

Samples a single formula.

Returns:

a single formula.

randomSample

public PlBeliefSet randomSample(int minLength,
                                int maxLength)

Specified by:

randomSample in class net.sf.tweety.commons.BeliefBaseSampler<PlBeliefSet>