/**
* Calculate the probability distribution for <b>P</b>(X<sub>i</sub> |
* mb(X<sub>i</sub>)), where mb(X<sub>i</sub>) is the Markov Blanket of
* X<sub>i</sub>. The probability of a variable given its Markov blanket is
* proportional to the probability of the variable given its parents times
* the probability of each child given its respective parents (see equation
* 14.12 pg. 538 AIMA3e):<br>
* <br>
* P(x'<sub>i</sub>|mb(Xi)) =
* αP(x'<sub>i</sub>|parents(X<sub>i</sub>)) *
* ∏<sub>Y<sub>j</sub> ∈ Children(X<sub>i</sub>)</sub>
* P(y<sub>j</sub>|parents(Y<sub>j</sub>))
*
* @param Xi
* a Node from a Bayesian network for the Random Variable
* X<sub>i</sub>.
* @param event
* comprising assignments for the Markov Blanket X<sub>i</sub>.
* @return a random sample from <b>P</b>(X<sub>i</sub> | mb(X<sub>i</sub>))
*/
public static double[] mbDistribution(Node Xi,
Map <RandomVariable, Object> evt)
{
FiniteDomain fd = (FiniteDomain)Xi.getRandomVariable().getDomain();
double[] X = new double[fd.size()];
for (int i = 0; i < fd.size(); i++)
{
// P(x'<sub>i</sub>|mb(Xi)) =
// αP(x'<sub>i</sub>|parents(X<sub>i</sub>)) *
// ∏<sub>Y<sub>j</sub> ∈ Children(X<sub>i</sub>)</sub>
// P(y<sub>j</sub>|parents(Y<sub>j</sub>))
double cprob = 1.0;
foreach (Node Yj in Xi.getChildren())
{
cprob *= Yj.getCPD().getValue(
getEventValuesForXiGivenParents(Yj, evt));
}
X[i] = Xi.getCPD()
.getValue(
getEventValuesForXiGivenParents(Xi,
fd.getValueAt(i), evt))
* cprob;
}
return(Util.normalize(X));
}
/**
*
* @param probabilityChoice
* a probability choice for the sample
* @param Xi
* a Random Variable with a finite domain from which a random
* sample is to be chosen based on the probability choice.
* @param distribution
* Xi's distribution.
* @return a Random Sample from Xi's domain.
*/
public static Object sample(double probabilityChoice, RandomVariable Xi,
double[] distribution)
{
FiniteDomain fd = (FiniteDomain)Xi.getDomain();
if (fd.size() != distribution.Length)
{
throw new ArgumentException("Size of domain Xi " + fd.size()
+ " is not equal to the size of the distribution "
+ distribution.Length);
}
int i = 0;
double total = distribution[0];
while (probabilityChoice > total)
{
i++;
total += distribution[i];
}
return(fd.getValueAt(i));
}
public Object getDomainValueAt(int idx)
{
return(varDomain.getValueAt(idx));
}