Particle structure

A particle is represented by the reb_particle structure in C. The python class Particle is an abstraction of the reb_particle structure in C. We will refer to both the C structure and the python object interchangeably as the particle structure and particle object.

The particle object contains the following variables which can be directly manipulated:

double m

mass

double r

physical radius of the particle

double x, y, z, vx, vy, vz

position and velocity coordinates

uint32_t hash

integer or hash value used to identify the particle

You can create a particle object which is not part of a REBOUND simulation.

CPython

struct reb_particle p = {.m=1., x=0., vy=0.};

p = rebound.Particle(m=1., x=0., vy=0.)

However, in most cases you will work with particles which have been added to a REBOUND simulation. You then access the particle using the simulation's particles array:

CPython

struct reb_simulation* r = reb_create_simulation();
// ... setup simulation, add particles ...
r->particles[0].x = 1;

sim = rebound.Simulation()
# ... setup simulation, add particles ... 
sim.particles[0].x = 1

Alternatively you can assign a hash value to particles and access them using the following syntax:

CPython

struct reb_simulation* r = reb_create_simulation();
reb_add_fmt(r, "m", 1.); 
r->particles[0].hash = reb_hash("star");
reb_add_fmt(r, "a", 1.); 
r->particles[1].hash = reb_hash("planet1");
struct reb_particle* p = reb_get_particle_by_hash(r, reb_hash("planet1"));

sim = rebound.Simulation()
sim.add(m=1., hash="star")
sim.add(a=1., hash="planet1")
p = sim.particles["planet1"]