double ComputeDelta(const vector<boost::shared_ptr<HypothesisInfo> >& pair) {
const double loss0 = pair[0]->features.dot(w) + pair[0]->cost - (pair[0]->oracle->features.dot(w) - pair[0]->oracle->cost);
const double loss1 = pair[1]->features.dot(w) + pair[1]->cost - (pair[1]->oracle->features.dot(w) - pair[1]->oracle->cost);
const double num = loss0 - loss1;
//const double num = pair[0]->loss - pair[1]->loss;
//cerr << "loss_0=" << pair[0]->loss << " loss_1=" << pair[1]->loss << endl;
cerr << " ComputeDelta: loss_0=" << loss0 << " loss_1=" << loss1;
SparseVector<double> diff = pair[0]->features;
diff -= pair[1]->features;
double diffsqnorm = diff.l2norm_sq();
double delta;
if (diffsqnorm > 0)
delta = num / (diffsqnorm * lr);
else
delta = 0;
cerr << " delta1=" << delta;
// clip
delta = max(-pair[0]->alpha, min(delta, pair[1]->alpha));
cerr << " delta2=" << delta << endl;
return delta;
}
