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.

##</code><code>##

C2 = (s3,m1,w3), with centroid(z) = w3

sim(w3,s3)=0.4
sim(w3,m1)=0.5
----------------+
   Total = 0.9
   |C2| = 3
Density = Total/|C2| = 0.9/3= 0.3