p: Population
Variable
Global
Population []
p = p + dt *( br - dr )

p in the updating graph: ( how to read )
In nodes
dt :
pi : population initial (people)
br : birth rate
dr : death rate
p : population
Out nodes
cig : capital-investment generation
cir : capital-investment ratio
cr : crowding ratio
nrur : natural-resource-usage rate
polg : pollution generation
br : birth rate
dr : death rate
p : population