In NLP, clustering has been used for virtually every semi-and unsupervised task, including POS tagging (Clark, 2003), labeled parse tree induction (Reichart and Rappoport, 2008), verb-type classification (Schulte im Walde, 2006), lexical acquisition (Davidov and Rappoport, 2006;Davidov and Rappoport, 2008), multilingual document clustering (Montavlo et al., 2006), coreference resolution (Nicolae and Nicolae, 2006) and named entity recognition (Elsner et al., 2009).
since we are not aware of any exact method for solving this problem, we use a hill-climbing algorithm.