VNode* DESPOT::Trial(VNode* root, RandomStreams& streams,
ScenarioLowerBound* lower_bound, ScenarioUpperBound* upper_bound,
const DSPOMDP* model, History& history, SearchStatistics* statistics) {
VNode* cur = root;
int hist_size = history.Size();
do {
if (statistics != NULL
&& cur->depth() > statistics->longest_trial_length) {
statistics->longest_trial_length = cur->depth();
}
ExploitBlockers(cur);
if (Gap(cur) == 0) {
break;
}
if (cur->IsLeaf()) {
double start = clock();
Expand(cur, lower_bound, upper_bound, model, streams, history);
if (statistics != NULL) {
statistics->time_node_expansion += (double) (clock() - start)
/ CLOCKS_PER_SEC;
statistics->num_expanded_nodes++;
statistics->num_tree_particles += cur->particles().size();
}
}
double start = clock();
QNode* qstar = SelectBestUpperBoundNode(cur);
VNode* next = SelectBestWEUNode(qstar);
if (statistics != NULL) {
statistics->time_path += (clock() - start) / CLOCKS_PER_SEC;
}
if (next == NULL) {
break;
}
cur = next;
history.Add(qstar->edge(), cur->edge());
} while (cur->depth() < Globals::config.search_depth && WEU(cur) > 0);
history.Truncate(hist_size);
return cur;
}
void DESPOT::Expand(QNode* qnode, ScenarioLowerBound* lb,
ScenarioUpperBound* ub, const DSPOMDP* model,
RandomStreams& streams,
History& history) {
VNode* parent = qnode->parent();
streams.position(parent->depth());
map<OBS_TYPE, VNode*>& children = qnode->children();
const vector<State*>& particles = parent->particles();
double step_reward = 0;
// Partition particles by observation
map<OBS_TYPE, vector<State*> > partitions;
OBS_TYPE obs;
double reward;
for (int i = 0; i < particles.size(); i++) {
State* particle = particles[i];
logd << " Original: " << *particle << endl;
State* copy = model->Copy(particle);
logd << " Before step: " << *copy << endl;
bool terminal = model->Step(*copy, streams.Entry(copy->scenario_id),
qnode->edge(), reward, obs);
step_reward += reward * copy->weight;
logd << " After step: " << *copy << " " << (reward * copy->weight)
<< " " << reward << " " << copy->weight << endl;
if (!terminal) {
partitions[obs].push_back(copy);
} else {
model->Free(copy);
}
}
step_reward = Discount(parent->depth()) * step_reward
- Globals::config.pruning_constant;//pruning_constant is used for regularization
double lower_bound = step_reward;
double upper_bound = step_reward;
// Create new belief nodes
for (map<OBS_TYPE, vector<State*> >::iterator it = partitions.begin();
it != partitions.end(); it++) {
OBS_TYPE obs = it->first;
logd << " Creating node for obs " << obs << endl;
VNode* vnode = new VNode(partitions[obs], parent->depth() + 1,
qnode, obs);
logd << " New node created!" << endl;
children[obs] = vnode;
history.Add(qnode->edge(), obs);
InitBounds(vnode, lb, ub, streams, history);
history.RemoveLast();
logd << " New node's bounds: (" << vnode->lower_bound() << ", "
<< vnode->upper_bound() << ")" << endl;
lower_bound += vnode->lower_bound();
upper_bound += vnode->upper_bound();
}
qnode->step_reward = step_reward;
qnode->lower_bound(lower_bound);
qnode->upper_bound(upper_bound);
qnode->utility_upper_bound = upper_bound + Globals::config.pruning_constant;
qnode->default_value = lower_bound; // for debugging
}