5. Dynamic weights

This 5th step illustrates how to obtain the shortest path from a point to another one and to update the weights of an existing graph.

Formulation

• At initialization, the value of the destruction_coeff of the road agents will be equal to 1.
• Add a new parameter: the destroy parameter that represents the value of destruction when a people agent takes a road. By default, it is equal to 0.02.
• When a people agent arrive at its destination (home or work), it updates the destruction_coeff of the road agents it took to reach its destination: "destruction_coeff = destruction_coeff - destroy". Then, the graph is updated.

Model Definition

global section

We add the destroy parameter.

In the global section, we define the destroy variable:

float destroy <- 0.02;

In the experiment section, we add a parameter:

parameter "Value of destruction when a people agent takes a road" var: destroy category: "Road" ;

We define a new reflex that updates the graph at each simulation step. For that, we use the with_weights operator. This operator allows to update the weights of an existing graph.

global {
    ...
    reflex update_graph{
        map<road,float> weights_map <- road as_map (each:: (each.destruction_coeff * each.shape.perimeter));
        the_graph <- the_graph with_weights weights_map;
     }
}

people agents

At each time-step, after a people agent has moved over one or multiple road segments, it updates the value of the destruction coefficient of road agents crossed (i.e. roads belonging to the path followed). We have for that to set the argument return_path to true in the goto action to obtain the path followed, then to compute the list of agents concerned by this path with the operator agent_from_geometry.

species people skills: [moving]{
    ...
    reflex move when: the_target != nil {
	path path_followed <- goto(target: the_target, on:the_graph, return_path: true);
	list<geometry> segments <- path_followed.segments;
	loop line over: segments {
	    float dist <- line.perimeter;
	    ask road(path_followed agent_from_geometry line) { 
		destruction_coeff <- destruction_coeff + (destroy * dist / shape.perimeter);
	    }
	}
	if the_target = location {
	    the_target <- nil ;
	}
    }
    ...
}	

Complete Model

model tutorial_gis_city_traffic

global {
    file shape_file_buildings <- file("../includes/building.shp");
    file shape_file_roads <- file("../includes/road.shp");
    file shape_file_bounds <- file("../includes/bounds.shp");
    geometry shape <- envelope(shape_file_bounds);
    float step <- 10 #mn;
    date starting_date <- date("2019-09-01-00-00-00");	
    int nb_people <- 100;
    int min_work_start <- 6;
    int max_work_start <- 8;
    int min_work_end <- 16; 
    int max_work_end <- 20; 
    float min_speed <- 1.0 #km / #h;
    float max_speed <- 5.0 #km / #h; 
    float destroy <- 0.02;
    graph the_graph;
	
    init {
	create building from: shape_file_buildings with: [type::string(read ("NATURE"))] {
	    if type="Industrial" {
		color <- #blue ;
	    }
	}
	create road from: shape_file_roads ;
	map<road,float> weights_map <- road as_map (each:: (each.destruction_coeff * each.shape.perimeter));
	the_graph <- as_edge_graph(road) with_weights weights_map;	
		
	list<building> residential_buildings <- building where (each.type="Residential");
	list<building> industrial_buildings <- building  where (each.type="Industrial") ;
	create people number: nb_people {
	    speed <- rnd(min_speed, max_speed);
	    start_work <- rnd (min_work_start, max_work_start);
	    end_work <- rnd(min_work_end, max_work_end);
	    living_place <- one_of(residential_buildings) ;
	    working_place <- one_of(industrial_buildings) ;
	    objective <- "resting";
	    location <- any_location_in (living_place); 
	}
    }
	
    reflex update_graph{
	map<road,float> weights_map <- road as_map (each:: (each.destruction_coeff * each.shape.perimeter));
	the_graph <- the_graph with_weights weights_map;
    }
}

species building {
    string type; 
    rgb color <- #gray ;
	
    aspect base {
	draw shape color: color ;
    }
}

species road  {
    float destruction_coeff <- rnd(1.0,2.0) max: 2.0;
    int colorValue <- int(255*(destruction_coeff - 1)) update: int(255*(destruction_coeff - 1));
    rgb color <- rgb(min([255, colorValue]),max ([0, 255 - colorValue]),0)  update: rgb(min([255, colorValue]),max ([0, 255 - colorValue]),0) ;
	
    aspect base {
	draw shape color: color ;
    }
}

species people skills:[moving] {
    rgb color <- #yellow ;
    building living_place <- nil ;
    building working_place <- nil ;
    int start_work ;
    int end_work  ;
    string objective ; 
    point the_target <- nil ;
		
    reflex time_to_work when: current_date.hour = start_work and objective = "resting"{
	objective <- "working" ;
	the_target <- any_location_in (working_place);
    }
		
    reflex time_to_go_home when: current_date.hour = end_work and objective = "working"{
	objective <- "resting" ;
	the_target <- any_location_in (living_place); 
    } 
	 
    reflex move when: the_target != nil {
	path path_followed <- goto(target: the_target, on:the_graph, return_path: true);
	list<geometry> segments <- path_followed.segments;
	loop line over: segments {
	    float dist <- line.perimeter;
	    ask road(path_followed agent_from_geometry line) { 
		destruction_coeff <- destruction_coeff + (destroy * dist / shape.perimeter);
	    }
	}
	if the_target = location {
	    the_target <- nil ;
	}
    }
	
    aspect base {
	draw circle(10) color: color border: #black;
    }
}

experiment road_traffic type: gui {
    parameter "Shapefile for the buildings:" var: shape_file_buildings category: "GIS" ;
    parameter "Shapefile for the roads:" var: shape_file_roads category: "GIS" ;
    parameter "Shapefile for the bounds:" var: shape_file_bounds category: "GIS" ;
    parameter "Number of people agents" var: nb_people category: "People" ;
    parameter "Earliest hour to start work" var: min_work_start category: "People" min: 2 max: 8;
    parameter "Latest hour to start work" var: max_work_start category: "People" min: 8 max: 12;
    parameter "Earliest hour to end work" var: min_work_end category: "People" min: 12 max: 16;
    parameter "Latest hour to end work" var: max_work_end category: "People" min: 16 max: 23;
    parameter "minimal speed" var: min_speed category: "People" min: 0.1 #km/#h ;
    parameter "maximal speed" var: max_speed category: "People" max: 10 #km/#h;
    parameter "Value of destruction when a people agent takes a road" var: destroy category: "Road" ;
	
    output {
	display city_display type:opengl {
	    species building aspect: base ;
	    species road aspect: base ;
	    species people aspect: base ;
	}
    }
}