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The C<AI::Categorizer::Learner> class is an abstract class that will
never actually be directly used in your code.  Instead, you will use a
subclass like C<AI::Categorizer::Learner::NaiveBayes> which implements
an actual machine learning algorithm.

The general description of the Learner interface is documented here.

=head1 METHODS

=over 4

=item new()

Creates a new Learner and returns it.  Accepts the following
parameters:

=over 4

=item knowledge_set

A Knowledge Set that will be used by default during the C<train()>
method.

=item verbose

If true, the Learner will display some diagnostic output while
training and categorizing documents.

=back

=item train()

=item train(knowledge_set => $k)

Trains the categorizer.  This prepares it for later use in
categorizing documents.  The C<knowledge_set> parameter must provide
an object of the class C<AI::Categorizer::KnowledgeSet> (or a subclass
thereof), populated with lots of documents and categories.  See
L<AI::Categorizer::KnowledgeSet> for the details of how to create such
an object.  If you provided a C<knowledge_set> parameter to C<new()>,
specifying one here will override it.

=item categorize($document)

Returns an C<AI::Categorizer::Hypothesis> object representing the
categorizer's "best guess" about which categories the given document
should be assigned to.  See L<AI::Categorizer::Hypothesis> for more
details on how to use this object.

=item categorize_collection(collection => $collection)

Categorizes every document in a collection and returns an Experiment
object representing the results.  Note that the Experiment does not
contain knowledge of the assigned categories for every document, only
a statistical summary of the results.

=item knowledge_set()

Gets/sets the internal C<knowledge_set> member.  Note that since the
knowledge set may be enormous, some Learners may throw away their
knowledge set after training or after restoring state from a file.

=item $learner-E<gt>save_state($path)

Saves the Learner for later use.  This method is inherited from
C<AI::Categorizer::Storable>.

=item $class-E<gt>restore_state($path)

Returns a Learner saved in a file with C<save_state()>.  This method
is inherited from C<AI::Categorizer::Storable>.

=back

=head1 AUTHOR

Ken Williams, ken@mathforum.org

=head1 COPYRIGHT

Copyright 2000-2003 Ken Williams.  All rights reserved.

This library is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.

=head1 SEE ALSO

AI::Categorizer(3)

=cut