aima.core.probability

Interface Factor

All Known Implementing Classes:

ProbabilityTable

public interface Factor

Artificial Intelligence A Modern Approach (3rd Edition): page 524.

Each factor is a matrix indexed by its argument variables.

Author:

Ciaran O'Reilly

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static interface	Factor.Iterator Interface to be implemented by an object/algorithm that wishes to iterate over the possible assignments for the random variables comprising this Factor.

Method Summary

Modifier and Type	Method and Description
boolean	contains(RandomVariable rv)
java.util.Set<RandomVariable>	getArgumentVariables()
double[]	getValues() Note: Do not modify the double[] returned by this method directly as it is intended to be read only.
void	iterateOver(Factor.Iterator fi) Iterate over all the possible value assignments for the Random Variables comprising this Factor.
void	iterateOver(Factor.Iterator fi, AssignmentProposition... fixedValues) Iterate over all possible values assignments for the Random Variables comprising this Factor that are not in the fixed set of values.
Factor	pointwiseProduct(Factor multiplier) Pointwise multiplication of this Factor by a given multiplier, creating a new Factor representing the product of the two. see: AIMA3e Figure 14.10 page 527. Note: Default Factor multiplication is not commutative.
Factor	pointwiseProductPOS(Factor multiplier, RandomVariable... prodVarOrder) Pointwise Multiplication - Product Order Specified (POS). see: AIMA3e Figure 14.10 page 527. Pointwise multiplication of this Factor by a given multiplier, creating a new Factor representing the product of the two.
Factor	sumOut(RandomVariable... vars) Sum out the provided variables from this Factor creating a new Factor of the remaining variables with their values updated with the summed out random variables. see: AIMA3e page 527.

Method Detail

getArgumentVariables

java.util.Set<RandomVariable> getArgumentVariables()

Returns:

a consistent ordered Set (e.g. LinkedHashSet) of the argument variables for this Factor.

contains

boolean contains(RandomVariable rv)

Parameters:

rv - the Random Variable to be checked.

Returns:

true if this Factor contains the passed in Random Variable, false otherwise.

getValues

double[] getValues()

Note: Do not modify the double[] returned by this method directly as it is intended to be read only.

Returns:

the double[] used to represent the Factor.

sumOut

Factor sumOut(RandomVariable... vars)

Sum out the provided variables from this Factor creating a new Factor of the remaining variables with their values updated with the summed out random variables.

see: AIMA3e page 527.

Parameters:

vars - the random variables to sum out.

Returns:

a new Factor containing any remaining random variables not summed out and a new set of values updated with the summed out values.

pointwiseProduct

Factor pointwiseProduct(Factor multiplier)

Pointwise multiplication of this Factor by a given multiplier, creating a new Factor representing the product of the two.

see: AIMA3e Figure 14.10 page 527.

Note: Default Factor multiplication is not commutative. The reason is because the order of the variables comprising a Factor dictate the ordering of the values for that factor. The default order of the variables of the Factor returned is the order of the variables as they are seen, as read from the left to right term, for e.g.:

f₁(Y)f₂(X, Y)

would give a Factor of the following form:
Y, X

i.e. an ordered union of the variables from the two factors.
To override the default order of the product use pointwiseProductPOS().

Parameters:

multiplier -

Returns:

a new Factor representing the pointwise product of this and the passed in multiplier. The order of the variables comprising the product factor is the ordered union of the left term (this) and the right term (multiplier).

See Also:

pointwiseProductPOS(Factor, RandomVariable...)

pointwiseProductPOS

Factor pointwiseProductPOS(Factor multiplier,
                           RandomVariable... prodVarOrder)

Pointwise Multiplication - Product Order Specified (POS).

see: AIMA3e Figure 14.10 page 527.

Pointwise multiplication of this Factor by a given multiplier, creating a new Factor representing the product of the two. The order of the variables comprising the product will match those specified.

Parameters:

multiplier -

prodVarOrder - the order the variables comprising the product are to be in.

Returns:

a new Factor representing the pointwise product of this and the passed in multiplier. The order of the variables comprising the product distribution is the order specified.

See Also:

pointwiseProduct(Factor)

iterateOver

void iterateOver(Factor.Iterator fi)

Iterate over all the possible value assignments for the Random Variables comprising this Factor.

Parameters:

fi - the Factor Iterator to iterate.

iterateOver

void iterateOver(Factor.Iterator fi,
                 AssignmentProposition... fixedValues)

Iterate over all possible values assignments for the Random Variables comprising this Factor that are not in the fixed set of values. This allows you to iterate over a subset of possible combinations.

Parameters:

fi - the Factor Iterator to iterate

fixedValues - Fixed values for a subset of the Random Variables comprising this Factor.