public DownsamplingUCTNode(
int maxplayer,
int minplayer,
GameState a_gs,
DownsamplingUCTNode a_parent,
long MAXACTIONS,
float bound)
throws Exception {
parent = a_parent;
gs = a_gs;
if (parent == null) depth = 0;
else depth = parent.depth + 1;
evaluation_bound = bound;
while (gs.winner() == -1
&& !gs.gameover()
&& !gs.canExecuteAnyAction(maxplayer)
&& !gs.canExecuteAnyAction(minplayer)) gs.cycle();
if (gs.winner() != -1 || gs.gameover()) {
type = -1;
} else if (gs.canExecuteAnyAction(maxplayer)) {
type = 0;
moveGenerator = new PlayerActionGenerator(a_gs, maxplayer);
moveGenerator.randomizeOrder();
} else if (gs.canExecuteAnyAction(minplayer)) {
type = 1;
moveGenerator = new PlayerActionGenerator(a_gs, minplayer);
moveGenerator.randomizeOrder();
} else {
type = -1;
System.err.println("RTMCTSNode: This should not have happened...");
}
}
public DownsamplingUCTNode UCTSelectLeaf(
int maxplayer, int minplayer, long MAXACTIONS, long cutOffTime, int max_depth)
throws Exception {
// Cut the tree policy at a predefined depth
if (depth >= max_depth) return this;
// Downsample the number of actions:
if (moveGenerator != null && actions == null) {
actions = new ArrayList<PlayerAction>();
children = new ArrayList<DownsamplingUCTNode>();
if (moveGenerator.getSize() > 2 * MAXACTIONS) {
for (int i = 0; i < MAXACTIONS; i++) {
actions.add(moveGenerator.getRandom());
}
} else {
PlayerAction pa = null;
long count = 0;
do {
pa = moveGenerator.getNextAction(cutOffTime);
if (pa != null) {
actions.add(pa);
count++;
if (count >= 2 * MAXACTIONS)
break; // this is needed since some times, moveGenerator.size() overflows
}
} while (pa != null);
while (actions.size() > MAXACTIONS) actions.remove(r.nextInt(actions.size()));
}
}
if (hasMoreActions) {
if (moveGenerator == null) return this;
if (children.size() >= actions.size()) {
hasMoreActions = false;
} else {
PlayerAction a = actions.get(children.size());
GameState gs2 = gs.cloneIssue(a);
DownsamplingUCTNode node =
new DownsamplingUCTNode(
maxplayer, minplayer, gs2.clone(), this, MAXACTIONS, evaluation_bound);
children.add(node);
return node;
}
}
// Bandit policy:
double best_score = 0;
DownsamplingUCTNode best = null;
for (int i = 0; i < children.size(); i++) {
DownsamplingUCTNode child = children.get(i);
double exploitation = ((double) child.accum_evaluation) / child.visit_count;
double exploration = Math.sqrt(Math.log((double) visit_count) / child.visit_count);
if (type == 0) {
// max node:
exploitation = (exploitation + evaluation_bound) / (2 * evaluation_bound);
} else {
exploitation = -(exploitation - evaluation_bound) / (2 * evaluation_bound);
}
double tmp = C * exploitation + exploration;
if (best == null || tmp > best_score) {
best = child;
best_score = tmp;
}
}
if (best == null) return this;
return best.UCTSelectLeaf(maxplayer, minplayer, MAXACTIONS, cutOffTime, max_depth);
}