Can we code to calculate the difference of tick values in netlogo - netlogo

Question

Actually i need to calculate density increase/decrease rate of human population for my model, the model is same as i asked in unable to make non-stationary turtles change their direction if an obstacle a patch ahead (a specific area and a building within it, people are randomly visiting and going). What i thought that i will be needing to save the tick values for initial population value and after some time difference updated population value. Below is the procedure i want to plot graph for.
to density-increase-rate
store population-density at some initial time (ticks)
store updated-population-density at some later-time (ticks)
calculate density-increase-rate
( ( ( updated-pd - previous-pd ) / (updated-tick - previous-tick ) ) * 100 ) / 10
end
I am calculating population-density in my code as
total-density-inside-boundary count people with [inside-boundary?]
for any suggestion or code help i am very thankful.

Answer 1

If you just want to plot this change, there is no need to store it because the plot will update each tick.
globals [total-density-inside-boundary density-increase-rate]
to calc-plot-vars
let old-density total-density-inside-boundary
set total-density-inside-boundary count people with [inside-boundary?]
set density-increase-rate (total-density-inside-boundary - old-density) / 100
end
Then have a plot on the interface with plot total-density-inside-boundary and plot density-increase-rate. You may need to do some rescaling to have them both on the same plot.
If you want to have the rate based on total time, then create a variable to hold the initial value and calculate it at the specific time you think initial means (such as the end of the setup or at a specific tick).
globals [total-density-inside-boundary initial-density]
to setup
... (commands that create your people)
set initial-density count people with [inside-boundary?]
...
end
to go
...
if ticks = 1 [ set initial-density count people with [inside-boundary?] ]
...
end
Then have the rate plot in the interface have plot (total-density-inside-boundary - initial-density) / 100