private Assignment doOnePass(FactorGraph mdl, Assignment initial) {
Assignment ret = (Assignment) initial.duplicate();
for (int vidx = 0; vidx < ret.size(); vidx++) {
Variable var = mdl.get(vidx);
DiscreteFactor subcpt = constructConditionalCpt(mdl, var, ret);
int value = subcpt.sampleLocation(r);
ret.setValue(var, value);
}
return ret;
}
// Warning: destructively modifies ret's assignment to fullAssn (I could save and restore, but I
// don't care
private DiscreteFactor constructConditionalCpt(
FactorGraph mdl, Variable var, Assignment fullAssn) {
List ptlList = mdl.allFactorsContaining(var);
LogTableFactor ptl = new LogTableFactor(var);
for (AssignmentIterator it = ptl.assignmentIterator(); it.hasNext(); it.advance()) {
Assignment varAssn = it.assignment();
fullAssn.setValue(var, varAssn.get(var));
ptl.setRawValue(varAssn, sumValues(ptlList, fullAssn));
}
ptl.normalize();
return ptl;
}
// backtracking search for a feasible assignment
private Assignment initialAssignmentRec(FactorGraph mdl, Assignment assn, int fi) {
if (fi >= mdl.factors().size()) return assn;
Factor f = mdl.getFactor(fi);
Factor sliced = f.slice(assn);
if (sliced.varSet().isEmpty()) {
double val = f.value(assn);
if (val > 1e-50) {
return initialAssignmentRec(mdl, assn, fi + 1);
} else {
return null;
}
}
for (AssignmentIterator it = sliced.assignmentIterator(); it.hasNext(); ) {
double val = sliced.value(it);
if (val > 1e-50) {
Assignment new_assn = Assignment.union(assn, it.assignment());
Assignment assn_ret = initialAssignmentRec(mdl, new_assn, fi + 1);
if (assn_ret != null) return assn_ret;
}
it.advance();
}
return null;
}
public Assignment sample(FactorGraph mdl, int N) {
// initForGraph (mdl);
Assignment assn = initialAssignment(mdl);
if (assn == null)
throw new IllegalArgumentException(
"GibbsSampler: Could not find feasible assignment for model " + mdl);
Timing timing = new Timing();
for (int i = 0; i < burnin; i++) {
assn = doOnePass(mdl, assn);
}
timing.tick("Burnin");
Assignment ret = new Assignment();
for (int i = 0; i < N; i++) {
assn = doOnePass(mdl, assn);
ret.addRow(assn);
}
timing.tick("Sampling");
return ret;
}
