Maybe a bug when computing entropy

When computing entropy value of Sr, according to the formula at page 10 of your publication "Ying Zhao and George Karypis. Criterion functions for document clustering: Experiments and analysis. Technical Report
TR #01–40, Department of Computer Science, University of Minnesota, Minneapolis, MN, 2001.", Entropy(Si) is define as -1/logq*sum(...). Here q is the number of classes in the dataset. However, I found that the vlaue is got by using k as q.