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=head1 DETAILS

The PAV algorithm is conceptually straightforward.  Given a set of training
cases ordered by the scores assigned by the classifier, it first assigns a
probability of one to each positive instance and a probability of zero to each
negative instance, and puts each instance in its own group.  It then looks, at
each iteration, for adjacent violators: adjacent groups whose probabilities
locally increase rather than decrease.  When it finds such groups, it pools
them and replaces their probability estimates with the average of the group's
values.  It continues this process of averaging and replacement until the
entire sequence is monotonically decreasing.  The result is a sequence of
instances, each of which has a score and an associated probability estimate,
which can then be used to map scores into probability estimates.

For further information on the PAV algorithm, you can read the section in my
paper referenced below.

=head1 EXPORT

This module exports three functions: calibrate, score_prob and print_mapping.