C1 = (s2,s3,m3,w3), with centroid(z) = s2

sim(s2,s3)=0.5
sim(s2,m3)=0.3
sim(s2,w3)=0.36
----------------+
   Total = 0.96
   |C1| = 4
Density = Total/|C1| = 0.96/4 = 0.24

we skip including this: sim(s2,s2)=1
We never compare a centroid with itself.