2. The method according to claim 1 wherein the cost function is a metric of dissimilarity between a first statistical distribution of likelihood of appearance by the plurality of document keywords in a typical document and a second statistical distribution of likelihood of appearance by the plurality of document keywords in a typical document, the second statistical distribution being approximated using proposed topic words.
2. The method according to claim 1 wherein the cost function is a metric of dissimilarity between a first statistical distribution of likelihood of appearance by the plurality of document keywords in a typical document and a second statistical distribution of likelihood of appearance by the plurality of document keywords in a typical document, the second statistical distribution being approximated using proposed topic words. 3. The method according to claim 2 wherein the metric of dissimilarity is cross-entropy.