For example, we estimate the conditional probability of linking not to ne...pas by considering the number of sentence pairs in which not occurs in the English sentence and both ne and pas occur in the French sentence, compared to the number of times not is linked to both ne and pas in pairs of corresponding sentences.
since evaluating each combination of parameter values in this way can take hours to days on a large training corpus, it seems safe to say that these parameters are rarely if ever truly jointly optimized for a particular alignment task.