Tikhonov, Ivanov and Morozov regularization for support vector machine learning

摘要

Learning according to the structural risk minimization principle can be naturally expressed as an Ivanov regularization problem. Vapnik himself pointed out this connection, when deriving an actual learning algorithm from this principle, like the well-known support vector machine, but quickly suggested to resort to a Tikhonov regularization schema, instead. This was, at that time, the best choice because the corresponding optimization problem is easier to solve and in any case, under certain hypothesis, the solutions obtained by the two approaches coincide. On the other hand, recent advances in learning theory clearly show that the Ivanov regularization scheme allows a more effective control of the learning hypothesis space and, therefore, of the generalization ability of the selected hypothesis. We prove in this paper the equivalence between the Ivanov and Tikhonov approaches and, for the sake of completeness, their connection to Morozov regularization, which has been show to be useful when effective estimation of the noise in the data is available. We also show that this equivalence is valid under milder conditions on the loss function with respect to Vapnik’s original proposal. These results allows us to derive several methods for performing SRM learning according to an Ivanov or Morozov regularization scheme, but using Tikhonov-based solvers, which have been thoroughly studied in the last decades and for which very efficient implementations have been proposed.