ClustEval clustering evaluation framework
The Fowlkes-Mallows Index is the geometric mean of precision and recall (see F-Score). This measure is based on the pairwise approach to calculate TP,TN,FP and FN. $FM = \sqrt{\frac{TP}{TP+FP} \cdot \frac{TP}{TP+FN}}$ In the binary classification background we have two classes that we want to distinguish: positive and negative. In this scenario there are four possible outcomes: