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Version: 1.8.1

9. Stopping condition

This 9th step illustrates how to use the pause action to stop a simulation.

Formulation

  • Addition of a stopping condition for the simulation: when there is no more prey or predator agents, the simulation stops

Model Definition

We add a new reflex that stops the simulation if the number of preys or the number of predators is zero.

global {
...
reflex stop_simulation when: (nb_preys = 0) or (nb_predators = 0) {
do pause ;
}
}

Complete Model

model prey_predator

global {
int nb_preys_init <- 200;
int nb_predators_init <- 20;
float prey_max_energy <- 1.0;
float prey_max_transfert <- 0.1;
float prey_energy_consum <- 0.05;
float predator_max_energy <- 1.0;
float predator_energy_transfert <- 0.5;
float predator_energy_consum <- 0.02;
float prey_proba_reproduce <- 0.01;
int prey_nb_max_offsprings <- 5;
float prey_energy_reproduce <- 0.5;
float predator_proba_reproduce <- 0.01;
int predator_nb_max_offsprings <- 3;
float predator_energy_reproduce <- 0.5;
int nb_preys -> {length(prey)};
int nb_predators -> {length(predator)};

init {
create prey number: nb_preys_init;
create predator number: nb_predators_init;
}

reflex stop_simulation when: (nb_preys = 0) or (nb_predators = 0) {
do pause;
}
}

species generic_species {
float size <- 1.0;
rgb color;
float max_energy;
float max_transfert;
float energy_consum;
float proba_reproduce;
int nb_max_offsprings;
float energy_reproduce;
image_file my_icon;
vegetation_cell my_cell <- one_of(vegetation_cell);
float energy <- rnd(max_energy) update: energy - energy_consum max: max_energy;

init {
location <- my_cell.location;
}

reflex basic_move {
my_cell <- choose_cell();
location <- my_cell.location;
}

reflex eat {
energy <- energy + energy_from_eat();
}

reflex die when: energy <= 0 {
do die;
}

reflex reproduce when: (energy >= energy_reproduce) and (flip(proba_reproduce)) {
int nb_offsprings <- rnd(1, nb_max_offsprings);
create species(self) number: nb_offsprings {
my_cell <- myself.my_cell;
location <- my_cell.location;
energy <- myself.energy / nb_offsprings;
}

energy <- energy / nb_offsprings;
}

float energy_from_eat {
return 0.0;
}

vegetation_cell choose_cell {
return nil;
}

aspect base {
draw circle(size) color: color;
}

aspect icon {
draw my_icon size: 2 * size;
}

aspect info {
draw square(size) color: color;
draw string(energy with_precision 2) size: 3 color: #black;
}
}

species prey parent: generic_species {
rgb color <- #blue;
float max_energy <- prey_max_energy;
float max_transfert <- prey_max_transfert;
float energy_consum <- prey_energy_consum;
float proba_reproduce <- prey_proba_reproduce;
int nb_max_offsprings <- prey_nb_max_offsprings;
float energy_reproduce <- prey_energy_reproduce;
image_file my_icon <- image_file("../includes/data/sheep.png");

float energy_from_eat {
float energy_transfert <- 0.0;
if(my_cell.food > 0) {
energy_transfert <- min([max_transfert, my_cell.food]);
my_cell.food <- my_cell.food - energy_transfert;
}
return energy_transfert;
}

vegetation_cell choose_cell {
return (my_cell.neighbors2) with_max_of (each.food);
}
}

species predator parent: generic_species {
rgb color <- #red;
float max_energy <- predator_max_energy;
float energy_transfert <- predator_energy_transfert;
float energy_consum <- predator_energy_consum;
float proba_reproduce <- predator_proba_reproduce;
int nb_max_offsprings <- predator_nb_max_offsprings;
float energy_reproduce <- predator_energy_reproduce;
image_file my_icon <- image_file("../includes/data/wolf.png");

float energy_from_eat {
list<prey> reachable_preys <- prey inside (my_cell);
if(! empty(reachable_preys)) {
ask one_of (reachable_preys) {
do die;
}
return energy_transfert;
}
return 0.0;
}

vegetation_cell choose_cell {
vegetation_cell my_cell_tmp <- shuffle(my_cell.neighbors2) first_with (!(empty(prey inside (each))));
if my_cell_tmp != nil {
return my_cell_tmp;
} else {
return one_of(my_cell.neighbors2);
}
}
}

grid vegetation_cell width: 50 height: 50 neighbors: 4 {
float max_food <- 1.0;
float food_prod <- rnd(0.01);
float food <- rnd(1.0) max: max_food update: food + food_prod;
rgb color <- rgb(int(255 * (1 - food)), 255, int(255 * (1 - food))) update: rgb(int(255 * (1 - food)), 255, int(255 * (1 - food)));
list<vegetation_cell> neighbors2 <- (self neighbors_at 2);
}

experiment prey_predator type: gui {
parameter "Initial number of preys: " var: nb_preys_init min: 0 max: 1000 category: "Prey";
parameter "Prey max energy: " var: prey_max_energy category: "Prey";
parameter "Prey max transfert: " var: prey_max_transfert category: "Prey";
parameter "Prey energy consumption: " var: prey_energy_consum category: "Prey";
parameter "Initial number of predators: " var: nb_predators_init min: 0 max: 200 category: "Predator";
parameter "Predator max energy: " var: predator_max_energy category: "Predator";
parameter "Predator energy transfert: " var: predator_energy_transfert category: "Predator";
parameter "Predator energy consumption: " var: predator_energy_consum category: "Predator";
parameter 'Prey probability reproduce: ' var: prey_proba_reproduce category: 'Prey';
parameter 'Prey nb max offsprings: ' var: prey_nb_max_offsprings category: 'Prey';
parameter 'Prey energy reproduce: ' var: prey_energy_reproduce category: 'Prey';
parameter 'Predator probability reproduce: ' var: predator_proba_reproduce category: 'Predator';
parameter 'Predator nb max offsprings: ' var: predator_nb_max_offsprings category: 'Predator';
parameter 'Predator energy reproduce: ' var: predator_energy_reproduce category: 'Predator';

output {
display main_display {
grid vegetation_cell lines: #black;
species prey aspect: icon;
species predator aspect: icon;
}

display info_display {
grid vegetation_cell lines: #black;
species prey aspect: info;
species predator aspect: info;
}

monitor "Number of preys" value: nb_preys;
monitor "Number of predators" value: nb_predators;
}
}