Sample frames from the Skeleton video. \\textbf{Left}: Four skeletons dancing in the same manner were manually segmented and tracked during a single one second interval. \n\\textbf{Center}: Affinity matrix before binarization. The slight differences in the entries are due to the intrinsic variability of the action itself. \\textbf{Right}: Binarized affinity matrix after applying the threshold $\\tau = 0.9/3= 0.3$. The values in the entries show slight variation but all larger than $0.3$, so they are all binarized to 1, and thus the four skeletons are grouped together.