double find_branch(exPtrs &p, Tree *t, Appear &app) {
double minTot = 10.0, minThr;
int minBra = -1;
for (Appear::IT it = app.B; it != app.E; it++) {
int i = *it; // i-th feature for branching
Comp comp(i);
sort(p.B, p.E, comp);
Unique u; // u stores Vm's
for (int j = 0; j < p.size(); j++)
u.insert(p[j]->feat[i]);
int yl = 0, nl = 0, yr = Y(p), nr = N(p);
exPtrs::IT k = p.B;
Unique::IT j = u.B, prev = j;
j++;
for ( ; j != u.E; j++) { // j-th threshold
double mid = ( *prev + *j ) / 2;
prev = j;
for ( ; k != p.E && (*k)->feat[i] < mid; k++) {
if ((*k)->ans > 0) yl++, yr--;
else nl++, nr--;
}
double curTot = total(yl, nl, yr, nr);
if (curTot < minTot) {
minTot = curTot;
minBra = i;
minThr = mid;
}
}
}
t->branch = minBra;
t->thresh = minThr;
return minBra;
}
