Package net.sf.tweety.logics.pl.util

Class SyntacticRandomSampler

java.lang.Object

net.sf.tweety.commons.BeliefSetSampler<PlFormula,PlBeliefSet>

net.sf.tweety.logics.pl.util.SyntacticRandomSampler

All Implemented Interfaces:

java.util.Iterator<PlBeliefSet>, BeliefSetIterator<PlFormula,PlBeliefSet>

public class SyntacticRandomSampler
extends BeliefSetSampler<PlFormula,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.BeliefSetSampler

DEFAULT_MAXIMUM_BELIEFBASE_LENGTH, DEFAULT_MINIMUM_BELIEFBASE_LENGTH

Constructor Summary

Constructors

Constructor	Description
SyntacticRandomSampler(Signature signature, Probability probneg, Probability probconj, Probability probdisj, double recDecrease)	Creates a new sampler.
SyntacticRandomSampler(Signature signature, Probability probneg, Probability probconj, Probability probdisj, double recDecrease, int minLength, int maxLength)	Creates a new sampler.

Method Summary

Modifier and Type	Method	Description
PlBeliefSet	next()	Returns the next belief set
PlFormula	sampleFormula(ProbabilityFunction<java.lang.Byte> prob)	Samples a single formula.

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

getMaxLength, getMinLength, getSamplerSignature, hasNext

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Iterator

forEachRemaining, remove

Constructor Detail

SyntacticRandomSampler

public SyntacticRandomSampler(Signature signature,
                              Probability probneg,
                              Probability probconj,
                              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.

SyntacticRandomSampler

public SyntacticRandomSampler(Signature signature,
                              Probability probneg,
                              Probability probconj,
                              Probability probdisj,
                              double recDecrease,
                              int minLength,
                              int maxLength)

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.

minLength - the minimum length of knowledge bases

maxLength - the maximum length of knowledge bases

Method Detail

sampleFormula

public PlFormula sampleFormula(ProbabilityFunction<java.lang.Byte> prob)

Samples a single formula.

Parameters:

prob - a probability function

Returns:

a single formula.

next

public PlBeliefSet next()

Returns the next belief set

Specified by:

next in interface BeliefSetIterator<PlFormula,PlBeliefSet>

Specified by:

next in interface java.util.Iterator<PlBeliefSet>

Specified by:

next in class BeliefSetSampler<PlFormula,PlBeliefSet>

Returns:

the next belief set