.density
: float
Density is defined as the ratio of the number of items to the total number of registered itemsets stored in .
> require 'zdd' > a=ZDD::itemset("a") > b=ZDD::itemset("b") > c=ZDD::itemset("c") # Total number of combinations using 3 items a,b,c is eight. # All combinations are stored in F in the expression below, with a density of 1.0. > f=(a+1)*(b+1)*(c+1) > f.show a b c + a b + a c + a + b c + b + c + 1 > puts f.density 1.0 # In the following, one set of combination (a b) is stored in F. # The density becomes 1/8=0.125.f=a*b > f.show a b c + a b + a c + a + b c + b + c + 1 > puts f.density 1.0 # When three sets of combinations (a b,a,b) are stored in F, the density becomes 3/8=0.375. > f+=a > f+=b > f.show a b c + a b + a c + 2 a + b c + 2 b + c + 1 > puts f.density 1.0