title: ValueError: Negative values in data passed to LatentDirichletAllocation.fit
body: <p>I'm trying to get the features sub-space that maximizes the separation between classes, using LDA, but the script raises the error  <code>ValueError: Negative values in data passed to LatentDirichletAllocation.fit</code></p>
  
  <p>I't cannot be used with negative data? Or what's the problem?
  I've been searching but no answers found...</p>