Pythagoras: A New Agent-based Simulation System - Northrop ...

Behavior-Change Triggers
Pythagoras: A New Agent-based Simulation System
The final feature of Pythagoras that is used to represent behavior is the behavior-change
event/action, or trigger. When an agent experiences one of the events/actions listed in
Table 3, the current behavior template is replaced by a new one, defined by new movement
and shooting desires, new color-change values, and a new set of behavior-change
triggers. For example, an agent can be set to walk up and down a street, as if on patrol,
but when the agent is shot at, his behavior changes to look for protective terrain, such as
a doorway.
To enhance behavior-change triggers, the user can decide how they will be applied.
A trigger can affect either an individual agent or a user-defined group of agents, or it
may cause an agent to order subordinates to change their behavior (for example, “Sound
the charge!”). For that purpose, leadership can be defined as either charismatic or
hierarchical:
• Under charismatic leadership, agents follow the highest or strongest leader.
• Under hierarchical leadership, agents follow the lowest ranking leader whom they
consider to be their leader (troops follow the sergeant, who follows the major, who
follows the general). Thus, orders can ripple through a group of agents, much as
they would in a military organization.
As usual in Pythagoras, the behavior-change threshold values are governed by soft rules,
so some agents will be more resistant to change. In addition, an agent can be assigned an
obedience value that determines, at random, whether the agent will accept or reject an
ordered behavior-change event/action.
Because the behavior template for an agent includes new triggers, and each template
is uniquely named, a series of templates can be constructed to represent a complex
behavior tree or network, with agents moving from one behavior to another as a scenario
Table 3. Currently implemented behavior-change triggers
Events/actions that cause agent to change behavior include
– Being shot at
– Detecting enemy
– Detecting friend
– Arriving at way point or objective
– Suffering friendly casualties (fewer than x%
known remaining)
– Losing leader (no leader within d)
– Red, green, or blue becoming greater or less than c
– Absolute time step
– Relative time step
Trigger reads new, complete, explicitly named behavior template (including setting
new triggers)
Delay before behavior takes effect (future capability), which simulates communication/
spinup time
x = Force strength
d = Distance
c = Color value
Technology Review Journal • Spring/Summer 2003 51