Second, the numerator and denominator are scaled by the function exp(ψ(•)), which reduces the probability of rare events.
the P choose distribution is estimated using expectations for each arc a dp,h,dir from head h to dependent POS tag d p in direction dir, and the update equation for P choose from iteration n to n + 1 is: where h is the head POS tag for the backoff distribution, and the head (word, POS) pair for the no backoff distribution.