MultiLevelArchitecture

Multi-level architecture

The multi-level architecture offers the modeler the following possibilities: the declaration of a species as a micro-species of another species, the representation of an entity as different types of agent (i.e., GAML species), the dynamic migration of agents between populations.

Index

• Declaration of micro-species
• Access to micro-agents / host agent
• Representation of an entity as different types of agent
• Dynamic migration of agents
• Example

Declaration of micro-species

A species can have other species as micro-species. The micro-species of a species is declared inside the species' declaration.

species macro_species {
      species micro_species_in_group {
      }
}

In the above example, micro_species_in_group is a micro-species of macro_species. An agent of macro_species can have agents micro_species_in_group as micro-agents. Agents of micro_species_in_group have an agent of macro_species as host agent.

As the species micro_species_in_group is declared inside the species macro_species, micro_species_in_group will return a list of micro_species_in_group agent inside the given macro_species agent.

global {
    init {
	create macro_species number:5;
    }
}

species macro_species  {	
    init {
	create micro_species_in_group number: rnd(10);
	write "the macro species agent named "+name+" contains "+length(micro_species_in_group)+" agents of micro-species.";
    }

    species micro_species_in_group { }
}

experiment my_experiment type: gui { }

In the above example, we create 5 macro-species agents, and each one creates a random number of inner micro-species agents. We can see that micro_species_in_group refers to the list of micro-species agents inside the given macro-species agent.

Access to micro-agents, host agent

To access micro-agents (from a macro-agent), and to host agent (from a micro-agents), you have to use two built-in attributes.

The members built-in attribute is used inside the macro-agent, to get the list of all its micro-agents.

species macro_species  {
    init {
	create first_micro_species number: 3;
	create second_micro_species number: 6;
	write "the macro-agent named "+name+" contains "+length(members)+" micro-agents.";
    }
	
    species first_micro_species { }
    
    species second_micro_species { }
}

The host built-in attribute is used inside a micro-agent to get its host macro-agent.

species macro_species {
	
    micro_species_in_group micro_agent;
	
    init {
	create micro_species_in_group number: rnd(10);
	write "the macro-agent named "+name+" contains "+length(members)+" micro-agents.";
    }
	
    species micro_species_in_group {
    	init {
    	    write "the micro-agent named "+name+" is hosted by "+host;
    	}
    }
}

NB: We already said that the world agent is a particular agent, instantiated just once. In fact, the world agent is the host of all the agents. You can try to get the host for a regular species agent, you will get the world agent itself (named as you named your model). You can also try to get the members of your world (from the global scope for example), and you will get the list of the agents presents in the world.

global {
    init {
	create macro_species number:5;
	write "the world has "+length(members)+" members.";
    }
}

species macro_species  {	
    init {
	write "the macro agent named "+name+" is hosted by "+host;
    }
}

Representation of an entity as different types of agent

The multi-level architecture is often used in order to represent an entity through different types of agent. For example, an agent "bee" can have a behavior when it is alone, but when the agent is near from a lot of agents, he can changes his type to "bee_in_swarm", defined as a micro-species agent of a macro-species "swarm" agent. Another example: an agent "pedestrian" can have a certain behavior when walking on the street, and then change his type to "pedestrian_in_building" when he is in a macro-agent "building".

You have then to distinguish two different species to define your micro-species:

• The first can be seen as a regular species (it is the "bee" or the "pedestrian" for instance). We will name this species as "micro_species".
• The second is the real micro-species, defined inside the macro-species (it is the "bee_in_swarm" or the "pedestrian_in_building" for instance). We will name this species as "micro_species_in_group". This species has to inherit from the "micro_species" in order to allow migrations between micro_species_in_group and micro_species.

species micro_species { }

species macro_species  {	
    species micro_species_in_group parent: micro_species { }
}

Dynamic migration of agents

In our example about bees, a "swarm" entity is composed of nearby flying "bee" entities. When a "bee" entity approaches a "swarm" entity, this "bee" entity will become a member of the group. To represent this, the modeler lets the "bee" agent change its species to "bee_in_swarm" species. The "bee" agent hence becomes a "bee_in_swarm" agent. To change species of an agent, we can use one of the following statements: capture, release, migrate.

The statement capture is used by the "macro_species" to capture one (or several) "micro_species" agent(s), and turn it (them) to a "micro_species_in_group". You can specify which agent (or list of agents) you want to capture by passing them as the first argument of the statement capture. The facet as is used to cast the agent(s) from "micro_species" to the species "micro_species_in_group". You can use the facet returns to get the newly captured agent(s).

capture agents_of_micro_species as: micro_species_in_group;

The statement release is used by a "macro_species" agent to release one (or several) "micro_species_in_group" agent(s), and turn it (them) to a "micro_species". You can specify which agent (or list of agents) you want to release by giving them as the first argument of the release statement. The facet as is used to cast the agents from "micro_species_in_group" species to "micro_species" species. The facet in is used to specify the new host (by default, it is the host of the "macro_species"). You can use the facet returns to get the newly released agent(s).

release agents_of_micro_species_in_group as: micro_species in: world;

The statement migrate, less used, permits agents to migrate from one population/species to another population/species and stay in the same host after the migration. Read the GAML Reference to learn more about this statement.

Example:

Here is an example of micro_species that gather together in macro_species when they are close enough.

model multilevel

global {
    int release_time <- 20;
    int capture_time <- 100;
    int remaining_release_time <- 0;
    int remaining_capture_time <- capture_time;
    init {
	create micro_species number:200;
    }
    reflex reflex_timer {
	if (remaining_release_time=1) {
	    remaining_release_time <- 0;
	    remaining_capture_time <- capture_time;
	} else if (remaining_capture_time=1) {
	    remaining_capture_time <- 0;
	    remaining_release_time <- release_time;
	}
	remaining_release_time <- remaining_release_time - 1;
	remaining_capture_time <- remaining_capture_time - 1;
    }
    reflex capture_micro_species when:(remaining_capture_time>0 and flip(0.1)) {
	ask macro_species {
	    list<micro_species> micro_species_in_range <- micro_species at_distance 1;
	    if (micro_species_in_range != []) {
		do capture_micro_species(micro_species_in_range);
	    }
	}
	ask micro_species {
	    list<micro_species> micro_species_list_to_be_captured <- micro_species at_distance 1;
	    if(micro_species_list_to_be_captured != []) {
		create macro_species {
		    location <- myself.location;
		    add myself to:micro_species_list_to_be_captured;
		    do capture_micro_species(micro_species_list_to_be_captured);
		}
	    }
	}
    }
}

species micro_species skills:[moving] {
    geometry shape <- circle(1);

    reflex move{
	do wander;
    }

    aspect base {
	draw shape border: #black;
    }	
}

species macro_species {
    geometry shape <- circle(1) update:circle(length(members));
	
    species micro_species_in_group parent:micro_species { }

    action capture_micro_species(list<micro_species> micro_list) {
	loop mic_sp over:micro_list {
	    capture mic_sp as:micro_species_in_group;
	}
    }
	
    reflex release_reflex when: (remaining_release_time>0 and flip(0.1)) {
	release members as: micro_species in:world;
	do die;
    }
	
    aspect base {
	draw shape border: #black;
	draw string(length(members)) color:#black size:4;
    }
}

experiment MyExperiment type: gui {
    output {
	display MyDisplay type: java2D {
	    species macro_species aspect: base;
	    species micro_species aspect: base;
	}
    }
}