Controlling lives of turtles in NetLogo - netlogo

Question

For a project, I'm developping a simulation in NetLogo dealing with rabies diseases in dogs and humans. I have some turtles-humans with dogs that can be vaccinated or not. At the beginning I create a dog with rabie and, in according to the fase (1 or 2) of the disease, it can spread the disease to other dogs with a probability. At the end the dog can die either for paralysis (if a probability is higher than 75%) or for other complications. Here's the code:
http://pastebin.com/esR75G3T
In the end you can see that a dog not dying for paralysis will die after some days (between 4 or 6). In other words when the days_infected are equal to end-life.
To check if everything is ok at the beginning I tried to set that NONE of the dog is vaccinated so everyone is supposed to get the disease. In fact when the dog is in phase 2 it will bite anyone. The problem is that if I delete the last line of the code, everything works and some dogs die of paralysis and the other remain alive. If I enable also the last line to let the other dogs die too, nothing works...no dog is infected. why?

Answer 1

This is not a problem with your code: this is a problem with the dynamics of your model. What's happening is that your initial sick dog dies before actually infecting another dog. This is why removing the if (days_infected = end-life) [die] "fixes" the problem.
When I tried your model with a huge population (e.g., 5000 people) so that encounters are more frequent, the infection does spread. You could also increase the probability of infection, or increase the duration of the "furious" phase, I guess.
Another unrelated suggestion, if I may: you should have distinct persons and dogs breeds. Trying to cram everything inside regular turtles makes your code much more complicated than it should be. The way I would approach this would be to create a link from the person to her dog, and then use tie so that the dog is automatically moved when you move the person.
Edit:
OK, here is a version of your code slightly modified to use breeds:
globals [
total_dogs_infected
total_dogs
dead_humans
dead_dogs
]
breed [ persons person ]
persons-own [
sick?
]
breed [ dogs dog ]
dogs-own [
sick?
vaccinated?
rabies_phase
days_infected
end-incubator
end-furious
end-life
]
to setup
clear-all
initialize-globals
setup-turtles
reset-ticks
end
to initialize-globals
set dead_humans 0
set dead_dogs 0
set total_dogs_infected 0
end
to setup-turtles
set-default-shape persons "person"
set-default-shape dogs "wolf"
create-persons people [
setxy random-xcor random-ycor
set size 1.5
set sick? false
ifelse random 100 < 43 [
set color green
hatch-dogs 1 [
set color brown
set heading 115 fd 1
create-link-from myself [ tie ]
set days_infected 0
set vaccinated? (random 100 > %_not_vaccinated)
if not vaccinated? [ set color orange ]
]
]
[
set color blue ;umano sano senza cane
]
]
set total_dogs count dogs
ask one-of dogs [ get_sick ]
end
to get_sick
set sick? true
set color white
set rabies_phase 1
set end-incubator 14 + random 57
set end-furious (end-incubator + random 5)
set end-life (end-furious + 4 + random 2)
set total_dogs_infected total_dogs_infected + 1
end
to go
move
infect
get-older-sick-dog
tick
end
to move
ask persons [
rt random 180
lt random 180
fd 1
]
end
to infect
ask dogs with [ sick? ] [
if (rabies_phase = 1 and (random 100) <= 2) or rabies_phase = 2 [
ask other dogs-here with [ not sick? and not vaccinated? ] [ get_sick ]
]
]
end
to get-older-sick-dog
ask dogs with [ sick? ] [
set days_infected days_infected + 1
;the incubator phase ends after at least 14 days + random(57) and then we have phase 2 (furious)
if (days_infected = end-incubator) [ set rabies_phase 2 ]
;when the main furious phase finishes we have 75% of probability that a secondary furious phase continues for other 4 - 6 days until death ;or we have a probability of 25% that the disease end in paralysis with a fast death
if (days_infected = end-furious and (random 100 > 75)) [
set dead_dogs dead_dogs + 1
die
]
if (days_infected = end-life) [
die
]
]
end
; These last reporters are not used,
; they just illustrate how to get the
; dog from the owner or vice-versa:
to-report my-dog ; person reporter
report one-of out-link-neighbors
end
to-report has-dog? ; person reporter
report any? out-link-neighbors
end
to-report my-owner ; dog reporter
report one-of in-link-neighbors
end
Not only does it simplify some expressions (e.g., ask dogs with [ sick? ] instead of ask turtles with [ has_dog? and sick_dog? ]), it opens up all sorts of possibilities: a dog could run away from its owner, the owner could die without the dog dying, an owner could have two dogs, etc.