22 essential terms in the vocabulary of particle systems and emergent simulation.
Alignment
A boids steering rule: steer toward the average velocity vector of neighboring agents within a vision radius. Produces flocking cohesion of direction.
Attractor
A point, line, or surface that pulls particles toward it — force typically proportional to inverse square of distance. Creates orbital and vortex behaviors.
Agent-Based System
A simulation composed of autonomous agents — each following its own local rules, with no global controller. Emergent behavior arises from agent interactions.
Boid
A simulated bird-like agent (Craig Reynolds, 1987). Exhibits flocking behavior through three local rules: separation, alignment, cohesion. The atomic unit of flocking simulation.
Brownian Motion
Random particle motion arising from thermal collisions. Modeled as a random walk — velocity perturbed by small random increments each frame. Produces organic, jittery drift.
Cohesion
A boids steering rule: steer toward the average position (center of mass) of neighbors within vision radius. Keeps the flock together without explicit tethering.
Drag
A friction force opposing velocity, proportional to speed. Applied as: velocity *= (1 - drag) per frame. Simulates air resistance, water viscosity, and general damping.
Emergence
Complex, unexpected global patterns arising from simple local rules. The flock has no leader; the ecosystem has no script. Structure emerges from interaction alone.
Euler Integration
The simplest numerical ODE solver: position += velocity * dt; velocity += acceleration * dt. Fast but accumulates error. Sufficient for visual particle simulations.
Flocking
Collective motion of a group of agents following only local interaction rules. Produces murmuration-like patterns. Studied in starlings, fish schools, and pedestrian crowds.
Force Field
A spatial function mapping position to a force vector — gravity (constant), wind (directional), turbulence (noise-based), vortex (rotational). Defines the invisible architecture particles navigate.
Lotka-Volterra
Differential equations modeling predator-prey population dynamics. Predator growth depends on prey density; prey declines with predator density. Produces cyclical population oscillations.
Mass
A scalar property of a particle. Determines resistance to acceleration (F=ma) and gravitational influence. Heavier particles accelerate more slowly and exert stronger gravitational fields.
Particle System
A collection of discrete point-like objects (particles) each with position, velocity, mass, and visual properties, evolved over time by force equations. Invented formally by William Reeves (1983).
Perlin Noise
Smooth, continuous pseudo-random function (Ken Perlin, 1983). Produces coherent variation across space — used for turbulence, terrain, and noise-driven force fields.
Predator-Prey
An ecological interaction where predator agents hunt prey agents. Population cycles emerge: predators increase → prey decline → predators starve → prey recover. Classic Lotka-Volterra dynamics.
Repeller
An attractor with negative force sign. Pushes particles away proportionally to proximity. Used for obstacle avoidance, explosion origins, and steering behaviors.
Reynolds Rules
The three rules of boids: Separation (avoid crowding), Alignment (match velocity), Cohesion (move toward center). Together, sufficient to produce convincing flocking behavior.
Separation
A boids steering rule: steer away from neighbors that are too close, within a smaller separation radius. Prevents collision and overcrowding within the flock.
Steering Behavior
An autonomous agent behavior producing a steering force toward a desired velocity or position. Includes seek, flee, arrive, pursue, evade, wander, and flock. Coined by Craig Reynolds.
Velocity Verlet
A more accurate integrator than Euler: updates position and velocity using average acceleration across the timestep. Better energy conservation — useful for orbital simulations.
Vortex
A rotational force field where particles orbit a center point. Force is perpendicular to the radius vector (tangential). Produces swirling, cyclone-like particle paths.