[edit]
Structured Prediction: From Gaussian Perturbations to Linear-Time Principled Algorithms
Proceedings of the 32nd Conference on Uncertainty in Artificial Intelligence, PMLR R14:228-235, 2016.
Abstract
Margin-based structured prediction commonly uses a maximum loss over all possible structured outputs (Altun & Hofmann, 2003; Collins, 2004; Taskar et al., 2003). In natural language processing, recent work (Zhang et al., 2014; Zhang et al., 2015) has proposed the use of the maximum loss over random structured outputs sampled independently from some proposal distribution. This method is linear-time in the number of random structured outputs and trivially parallelizable. We study this family of loss functions in the PAC-Bayes framework under Gaussian perturbations (McAllester, 2007). Under some technical conditions and up to statistical accuracy, we show that this family of loss functions produces a tighter upper bound of the Gibbs decoder distortion than commonly used methods. Thus, using the maximum loss over random structured outputs is a principled way of learning the parameter of structured prediction models. Besides explaining the experimental success of (Zhang et al., 2014; Zhang et al., 2015), our theoretical results show that more general techniques are possible.