/**
* computes a hash-backed policy for every state visited along the greedy path of the UCT tree.
*/
public void computePolicyFromTree() {
policy = new HashMap<StateHashTuple, GroundedAction>();
if (this.planner.getRoot() == null) {
return;
}
// define policy for all states that are expanded along the greedy path of the UCT tree
LinkedList<UCTStateNode> queue = new LinkedList<UCTStateNode>();
queue.add(planner.getRoot());
while (queue.size() > 0) {
UCTStateNode snode = queue.poll();
if (!planner.containsActionPreference(snode)) {
System.out.println(
"UCT tree does not contain action preferences of the state queried by the UCTTreeWalkPolicy. Consider replanning with planFromState");
break; // policy ill defined
}
UCTActionNode choice = this.getQGreedyNode(snode);
if (choice != null) {
policy.put(snode.state, choice.action); // set the policy
List<UCTStateNode> successors =
choice.getAllSuccessors(); // queue up all possible successors of this action
for (UCTStateNode suc : successors) {
queue.offer(suc);
}
}
}
}
@Override
public boolean isDefinedFor(State s) {
if (policy == null) {
this.computePolicyFromTree();
}
GroundedAction ga = policy.get(planner.stateHash(s));
if (ga == null) {
return false;
}
return true;
}
@Override
public AbstractGroundedAction getAction(State s) {
if (policy == null) {
this.computePolicyFromTree();
}
GroundedAction ga = policy.get(planner.stateHash(s));
if (ga == null) {
throw new PolicyUndefinedException();
}
return ga;
}
@Override
public List<ActionProb> getActionDistributionForState(State s) {
if (policy == null) {
this.computePolicyFromTree();
}
GroundedAction ga = policy.get(planner.stateHash(s));
if (ga == null) {
throw new PolicyUndefinedException();
}
List<ActionProb> res = new ArrayList<Policy.ActionProb>();
res.add(new ActionProb(ga, 1.)); // greedy policy so only need to supply the mapped action
return res;
}
