ZDD : Overview of ZDD Operators and Methods : density : Compute the density of ZDD

3.18 density : Compute the density of ZDD

Format

$obj$ .density $\rightarrow$ $dens$

$dens$ : float

Description

Density is defined as the ratio of the number of items to the total number of registered itemsets stored in $obj$ .

Example

Example 1: Basic Example

> 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

See Also