Many semi-supervised learning algorithms only
deal with binary classification. Their extension to the
multi-class problem is usually obtained by repeatedly
solving a set of binary problems. Additionally, many
of these methods do not scale very well with respect
to a large number of unlabeled samples, which limits
their applications to large-scale problems with many
classes and unlabeled samples.
In this paper, we directly address the multi-class
semi-supervised learning problem by an efficient
boosting method. In particular, we introduce a new
multi-class margin-maximizing loss function for the
unlabeled data and use the generalized expectation
regularization for incorporating cluster priors into
the model. Our approach enables efficient usage of
very large data sets. The performance and efficiency
of our method is demonstrated on both standard machine
learning data sets as well as on challenging
object categorization tasks.