Contrastive Estimation

This is a method proposed by Smith and Eisner 2005:Contrastive Estimation: Training Log-Linear Models on Unlabeled Data.

The proposed approach deals with the estimation of log-linear models (e.g. Conditional Random Fields) in an unsupervised fashion. The method focuses on the denominator $\sum _{x\prime ,y\prime }p(x\prime ,y\prime )$ of the log-linear models by exploiting the so called implicit negative evidence.