sidef-scripts/Other/mortality-natality_simulation.sf

#!/usr/bin/ruby

# Naive simulation of world population decrease when the mortality rate is greater than the natality rate.

var population = 7.7e9      # world population

var deaths = 61e6           # deaths per year
var births = deaths/5       # births per year
var target = 500_000_000    # target population

var death_rate = deaths/population.float
var birth_rate = births/population.float

var years = 0

while (population > target) {
    population -= population*death_rate
    population += population*birth_rate
    ++years
}

say "It took #{years} years to reach a population of #{target.commify}."

__END__
It took 430 years to reach a population of 500,000,000.