title: Porter stemmer gives different results when calculating semantic similarity
body: <p>I am  making some tests with ws4j library. In particular I want to calculate similarity between two test words "university" and "teaching". When I apply stemming, it gives me 0 similarity... When I do not apply stemming, the result is higher than 0.
  On the other hand, when I check the similarity between "genders" and "sex", then stemming has a reverse impact: when I use it, it gives a positive similarity. Otherwise the similarity is equal to 0.</p>
  
  <p>Why does it happen and which would be a more generic approach that would give similar results for both examples? </p>
  
  <pre><code>public class TestWs4j
  {    
      private static ILexicalDatabase db = new NictWordNet();
      private static RelatednessCalculator[] rcs = {
              new WuPalmer(db), // new HirstStOnge(db), new LeacockChodorow(db), new Lesk(db),
              new JiangConrath(db), new Path(db) // new Resnik(db), new Lin(db),
      };
  
      private static void run( String word1, String word2 ) {
          WS4JConfiguration.getInstance().setMFS(true);
          for ( RelatednessCalculator rc : rcs ) {
              double s = rc.calcRelatednessOfWords(word1, word2);
              System.out.println( rc.getClass().getName()+"\t"+s );
          }
      }
      public static void main(String[] args) {
          long t0 = System.currentTimeMillis();
          PorterStemmer stemmer = new PorterStemmer();
  //        String w1 = stemmer.stemWord("university");
  //        String w2 = stemmer.stemWord("teaching");
  //        run(w1,w2);
          run("university","teaching");
          long t1 = System.currentTimeMillis();
          System.out.println( "Done in "+(t1-t0)+" msec." );
      }
  }
  </code></pre>