11. Writing Files

This 11th step Illustrates how to save data in a text file.

Formulation

At each simulation step, write in a text file:
- The time step
- The number of prey and predator agents
- The min and max energy of the prey and predator agents

Model Definition

global section

GAMA provides several ways to write file.

A first ways consist in using the statement file in the output section: at each simulation step, the expression given is written in the given file.

   file file_name type: file_type data: data_to_write;

With:

file_name: string (by default the file in saved in the /models/ of your project directory)
file_type: string

There are 2 possible types :

‘txt’ (text) : in that case, my_data is treated as a string, which is written directly in the file
‘csv’ : in that case, my_data is treated as a list of variables to write : [“var1”, “var2”, “var3”].

A second way to write file consists in using the save statement:

   save my_data type: file_type to: file_name;

With:

file_type : string
file_name : string

There are 3 possible types :

‘shp’ (shapefile - GIS data) : in that case, my_data is treated as a list of agents : all their geometries are saved in the file (with some variables as attributes)
‘txt’ (text) : in that case, my_data is treated as a string, which is written directly in the file
‘csv’ : in that case, my_data is treated as a list of values : [val1, val2, val3].

We use this statement (in a global reflex called save_result) to write:

The cycle step: use of the cycle keyword that returns the current simulation step.
The number of prey and predator agents: use of nb_preys and nb_predators variables

The min and max energy of the prey and predator agents: use of list min_of expression and list max_of expression keywords. In addition, we verify with the tertiary operator (condition ? val_if : val_else).

reflex save_result when: (nb_preys > 0) and (nb_predators > 0){
save ("cycle: "+ cycle + "; nbPreys: " + nb_preys
    + "; minEnergyPreys: " + ((prey as list) min_of each.energy)
    + "; maxSizePreys: " + ((prey as list) max_of each.energy) 
   	+ "; nbPredators: " + nb_predators           
   	+ "; minEnergyPredators: " + ((predator as list) min_of each.energy)          
   	+ "; maxSizePredators: " + ((predator as list) max_of each.energy)) 
   	to: "results.txt" type: "text" ;
}

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 save_result when: (nb_preys > 0) and (nb_predators > 0){
		save ("cycle: "+ cycle + "; nbPreys: " + nb_preys
			+ "; minEnergyPreys: " + ((prey as list) min_of each.energy)
			+ "; maxSizePreys: " + ((prey as list) max_of each.energy) 
	   		+ "; nbPredators: " + nb_predators           
	   		+ "; minEnergyPredators: " + ((predator as list) min_of each.energy)          
	   		+ "; maxSizePredators: " + ((predator as list) max_of each.energy)) 
	   		to: "results.txt" type: "text" ;
	}
	
	reflex stop_simulation when: (nb_preys = 0) or (nb_predators = 0) {
		do halt ;
	} 
}

species generic_species {
	float size <- 1.0;
	rgb color  ;
	float max_energy;
	float max_transfert;
	float energy_consum;
	float proba_reproduce ;
	float nb_max_offsprings;
	float energy_reproduce;
	file my_icon;
	vegetation_cell myCell <- one_of (vegetation_cell) ;
	float energy <- (rnd(1000) / 1000) * max_energy  update: energy - energy_consum max: max_energy ;
	
	init {
		location <- myCell.location;
	}
		
	reflex basic_move {
		myCell <- choose_cell();
		location <- myCell.location; 
	} 
	
	vegetation_cell choose_cell {
		return nil;
	}
		
	reflex die when: energy <= 0 {
		do die ;
	}
	
	reflex reproduce when: (energy >= energy_reproduce) and (flip(proba_reproduce)) {
		int nb_offsprings <- 1 + rnd(nb_max_offsprings -1);
		create species(self) number: nb_offsprings {
			myCell <- myself.myCell ;
			location <- myCell.location ;
			energy <- myself.energy / nb_offsprings ;
		}
		energy <- energy / nb_offsprings ;
	}
	
	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 ;
	file my_icon <- file("../images/predator_prey_sheep.png") ;
		
	reflex eat when: myCell.food > 0 {
		float energy_transfert <- min([max_transfert, myCell.food]) ;
		myCell.food <- myCell.food - energy_transfert ;
		energy <- energy + energy_transfert ;
	}
	
	vegetation_cell choose_cell {
		return (myCell.neighbours) 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 ;
	list<prey> reachable_preys update: prey inside (myCell);
	float proba_reproduce <- predator_proba_reproduce ;
	int nb_max_offsprings <- predator_nb_max_offsprings ;
	float energy_reproduce <- predator_energy_reproduce ;
	file my_icon <- file("../images/predator_prey_wolf.png") ;
	
	reflex eat when: ! empty(reachable_preys) {
		ask one_of (reachable_preys) {
			do die ;
		}
		energy <- energy + energy_transfert ;
	}
	
	vegetation_cell choose_cell {
		vegetation_cell myCell_tmp <- shuffle(myCell.neighbours) first_with (!(empty (prey inside (each))));
		if myCell_tmp != nil {
			return myCell_tmp;
		} else {
			return one_of (myCell.neighbours);
		} 
	}
}
	
grid vegetation_cell width: 50 height: 50 neighbours: 4 {
	float maxFood <- 1.0 ;
	float foodProd <- (rnd(1000) / 1000) * 0.01 ;
	float food <- (rnd(1000) / 1000) max: maxFood update: food + foodProd ;
	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> neighbours  <- (self neighbours_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 ;
		}
		display Population_information refresh:every(5) {
			chart "Species evolution" type: series size: {1,0.5} position: {0, 0} {
				data "number_of_preys" value: nb_preys color: #blue ;
				data "number_of_predator" value: nb_predators color: #red ;
			}
			chart "Prey Energy Distribution" type: histogram background: rgb("lightGray") size: {0.5,0.5} position: {0, 0.5} {
				data "]0;0.25]" value: prey count (each.energy <= 0.25) color:#blue;
				data "]0.25;0.5]" value: prey count ((each.energy > 0.25) and (each.energy <= 0.5)) color:#blue;
				data "]0.5;0.75]" value: prey count ((each.energy > 0.5) and (each.energy <= 0.75)) color:#blue;
				data "]0.75;1]" value: prey count (each.energy > 0.75) color:#blue;
			}
			chart "Predator Energy Distribution" type: histogram background: rgb("lightGray") size: {0.5,0.5} position: {0.5, 0.5} {
				data "]0;0.25]" value: predator count (each.energy <= 0.25) color: #red ;
				data "]0.25;0.5]" value: predator count ((each.energy > 0.25) and (each.energy <= 0.5)) color: #red ;
				data "]0.5;0.75]" value: predator count ((each.energy > 0.5) and (each.energy <= 0.75)) color: #red ;
				data "]0.75;1]" value: predator count (each.energy > 0.75) color: #red;
			}
		}
		monitor "Number of preys" value: nb_preys;
		monitor "Number of predators" value: nb_predators;
	}
}