title: Gensim LDA: coherence values not reproducible between runs
body: <p>I used this code, <a href="https://datascienceplus.com/evaluation-of-topic-modeling-topic-coherence/" rel="nofollow noreferrer">https://datascienceplus.com/evaluation-of-topic-modeling-topic-coherence/</a>, to find topic coherence for a dataset. When I tried this code with the same number of topics, I got new values after each running. For example, for the number of topics =10, I got the following value after 2 running:</p>
  
  <p>First Run for the number of topics =10
  Coherence Score CV_1:  0.31230269562327095</p>
  
  <p>Coherence Score UMASS_1:  -3.3065236823786064</p>
  
  <p>Second Run the number of topics =10
  Coherence Score CV_2:  0.277016662550274</p>
  
  <p>Coherence Score UMASS_2:  -3.6146150653617743</p>
  
  <p>What is the reason? In this unstable case, how we can trust this library? The highest coherence value changed as well.  </p>