Sunday, February 28, 2010
Combining discriminative and Generative training
This blog is a continuation of the previous post Targeting discrimination as opposed to similarity. In model learning, given labeled data there is always a choice to make, discriminative or generative. There are pros and cons of either methods and usually a two-stage approach is used to combine the power of the two. I found a very recent paper, Multi-Conditional Learning published in AAAI 2006, on combining the power of the two at the time of learning. The likelihood function is now composed of the generative likelihood and the discriminative likelihood. This is possible only because we have labeled data. The discriminative-generative pair used for illustration is primarily the CRF-MRF. The MRF is used to capture topic co-occurrences. The word co-occurrences are captured by the latent topic model. However, by using a MCL regularizer (discriminative component) in the learning algorithm, the model being learnt is actually a combination of MRF and CRF, thereby combining the power of the two.The authors claim huge performance gains in document retrieval on the 20newsgroups dataset.