title: Input documents to LDA
body: <p>Assume I have N text documents and I run LDA in the following 2 ways,</p>
  
  <ul>
  <li>run LDA over the N documents at once</li>
  <li>run on each document separately, so for N documents you run the algorithm N times</li>
  </ul>
  
  <p>I'm aware of what number of topics to choose as well; in the first case i can select N to be the number of topics (assuming each document is about a single topic) but if I run it on each document separately not sure how to select the number of topics as well...?</p>
  
  <p>What's going on in these two cases?</p>