The Pessimistic Limits and Possibilities of Margin-based Losses in   Semi-supervised Learning
  Consider a classification problem where we have both labeled and unlabeled data available. We show that for linear classifiers defined by convex margin-based surrogate losses that are decreasing, it is impossible to construct any semi-supervised approach that is able to guarantee an improvement over the supervised classifier measured by this surrogate loss on the labeled and unlabeled data. For convex margin-based loss functions that also increase, we demonstrate safe improvements are possible. 
Jesse H. Krijthe and Marco Loog
stat.ML cs.LG