How to update a proportion used to select among turtles in a loop? - netlogo

Question

In my model the turtles have two sexes and there are two potential strategies "0" and "1". The females count the number of males in a set radius and choose among that pool based on their strategies.
The females have a limit to their pool of potential mates and they loop through this pool to select the males according to their strategy. This is all in the to-choose procedure.
One issue that a colleague picked up on is that the following line of code should be updated every time a female chooses another mate so that the proportion reflects the remaining potential mates and not the n-max which was set outside of the loop.
set prop_B ( count availa-males with [ strategy = 0 ] ) / n-max
To state the issue another way for clarity if the n-max is 5 and a female sets the prop_B using this value for the first mate then in the next iteration of the loop n-max should deprecate by 1 because there are only 4 remaining males.
So it should be something like: set prop_B ( count availa-males with [ strategy = 0 ] ) / (n-max - count mates-already-chosen)
Please see below for a working example of the model. Hope you can help.
turtles-own [sex availa-males mates mate-count max-mate-count strategy n-max prop_B proba_B]
breed [males male]
breed [females female]
to setup
clear-all
create-males 50
create-females 1
ask turtles [
setxy random-xcor random-ycor
ifelse random 2 = 1 [set strategy 1] [set strategy 0]
]
ask males [set color red]
ask females [set color blue]
reset-ticks
end
to go
ask males [
; fd 1
]
ask turtles [
set mates ( turtle-set )
]
ask females [choose]
tick
end
to choose
; set a cap on possible mates for females; 5, or the number
; available within the radius if less than 5
set availa-males males in-radius 5
set n-max count availa-males
set max-mate-count ifelse-value ( n-max < 5 ) [ n-max ] [ 5 ] ; 5 5
; Until a female has chosen up to her maximum number of mates:
while [ mate-count < max-mate-count ]
[; determine which available males are not already in her 'mates' agentset
set availa-males availa-males with [ not member? self [mates] of myself ]
; assess the proportion of the '0' strategy in remaining available males
set prop_B ( count availa-males with [ strategy = 0 ] ) / n-max
; example probability choice, just meant to choose '0 strategy' males
; with a frequency disproportionate to availability
set proba_B ifelse-value ( prop_B <= 0.1 ) [ 0.8 ] [ 0.2 ]
; use a random float to determine which strategy type is chosen
set mates ( turtle-set mates
ifelse-value ( random-float 1 < proba_B )
[ one-of availa-males with [ strategy = 0] ]
[ one-of availa-males with [ strategy = 1]] )
; count the current mates to break the while loop once
; the maximum number of mates is reached
set mate-count count mates
]
; have the female's males add her to their own mates agentset
ask mates [ set mates ( turtle-set mates myself ) ]
if n-max < count mates [ print "Fewer available males than mates" ]
end

Answer 1

Since you don't need them to be selected sequentially, then one option you should think about is the weighted equivalent of n-of from the rnd extension. The following code is a complete model that uses weighted selection, to show you how it could work. But it won't give quite the same results as your approach. Your mathematics basically forces one choice or the other based on the proportion of each. I thought that might work for you anyway, as the weighting is just a demonstration of disproportional.
extensions [rnd]
turtles-own
[ sex
mates
strategy
]
breed [males male]
breed [females female]
to setup
clear-all
create-males 50 [set color red set sex "M"]
create-females 1 [set color blue set sex "F"]
ask turtles
[ setxy random-xcor random-ycor
set strategy one-of [1 0]
set mates nobody
]
reset-ticks
end
to go
ask males
[ ; fd 1
]
ask females [choose]
tick
end
to choose
let availa-males males in-radius 5
let max-mate-count min (list 5 count availa-males)
if max-mate-count < 5 [ print "Fewer available males than mates" ]
let new-mates rnd:weighted-n-of max-mate-count availa-males [ strategy-weight strategy ]
set mates (turtle-set mates new-mates)
ask new-mates
[ set mates (turtle-set mates myself)
]
end
to-report strategy-weight [ #strategy ]
if #strategy = 1 [ report 0.2 ]
if #strategy = 0 [ report 0.8 ]
report 0
end
You will notice I also removed a bunch of turtle variables. You don't need to have a permanent variable, just create a temporary one with let. I also noticed you have sex as a turtle variable, but you are actually handling sex with different breeds, but I left it in just in case it has some other purpose.