stellaris math rambling //
population grows by points. when a planet has (100 + 0.25 * empire population) growth points, it gets spends that many growth points & gets a new pop.
if the wiki is to be believed (and I'm not sure it is), growth points per month is
3/8 * pop * (1 - pop/cap) - 3/8
up to a maximum of +4.5/month, where pop is the number of pops on the planet & cap is the planetary housing available.
I'm pretty sure that's not right for v3.4, because planets with 1 pop still grow.
correct stellaris math //
yep wiki is completely incorrect for v3.4
in v3.4, base population growth is
pop =< 10: 3
pop > 10: 3 + ???(population, capacity, "logistic growth cap" = +1.50)
where the unknown function is presented as a bonus "because you have a balance between population and capacity"
for high population planets (40+), the bonus will stay at +1.50 even if the planet is overpopulated (pops > housing) up until some threshold (pops > 1.25 * housing?) when growth stops completely
stellaris immigration rambling //
immigration/emigration is added directly to the base rate of 3~4.5
the game tracks some kind of net migration flux based on each planet's "immigration pull" and "emigration push" score [so you might get -1.3 on the homeworld and +0.8 & +0.5 on two colonies]
it does not track species or biome; the rate is added/subtracted from whatever species happens to be growing on each planet: if -1.0 desert snakes emigrate, +1.0 arctic fish will immigrate.
