title: Dynamic number of topics in topic models
body: <p>I am new to topic modelling.
  My aim is to find key topics from a document. I am planning to use lda for the purpose. But in lda the number of topics should be predefined.I believe if a document from some other domain which was not in the training corpus comes,it will not give proper results. Is there any alternative solution? Is my thought is correct?    </p>