Removing particles

Removing all particles

You can remove all particles with the following code:

CPython

struct reb_simulation* r = reb_simulation_create();
// ... add particles ...
reb_simulation_remove_all_particles(r);

sim = rebound.Simulation()
# ... add particles ...
del sim.particles

Remove particle by index

Each particle in a REBOUND simulation can be uniquely identified with its position in the particles array, its index. You can remove a particle using this index as shown in the following code:

CPython

struct reb_simulation* r = reb_simulation_create();
reb_simulation_add_fmt(r, "m", 1.); // star, index=0
reb_simulation_add_fmt(r, "a", 1.); // planet 1, index=1
reb_simulation_add_fmt(r, "a", 2.); // planet 2, index=2
reb_simulation_remove_particle(r, 1, 1); // removes planet 1 (index 1)

The first argument of reb_simulation_remove_particle is the simulation from which you want to remove the particle. The second argument is the index of the particle. The third argument determines if you want to keep the particle array sorted. In most cases you want to (set the argument to 1). For simulation with many particles (millions), this might be slow. In that case set this argument to 0.

The function returns 0 if the particle was successfully removed, and 1 otherwise.

sim = rebound.Simulation()
sim.add(m=1.) // star, index=0
sim.add(a=1.) // planet 1, index=1
sim.add(a=2.) // planet 2, index=2
sim.remove(1)

The order of the remaining particles will remain unchanged. (In previous versions of REBOUND this was the behaviour when keep_sorted=1 was set. This is now the default.)

Remove particle by name

In addition to the index, you can also identify particles by name. This is useful when you want to make sure you can uniquely identify particles in simulations where you constantly add or remove particles. If a particle has a name, you can remove it as shown here:

CPython

struct reb_simulation* r = reb_simulation_create();
reb_simulation_add_fmt(r, "m name", 1., "star"); 
reb_simulation_add_fmt(r, "a name", 1., "planet1"); 
reb_simulation_add_fmt(r, "a name", 2., "planet2"); 
reb_simulation_remove_particle_by_name(r, "planet1");

The syntax of the function is the same as for reb_simulation_remove_particle except you pass the name instead of the index.

sim = rebound.Simulation()
sim.add(m=1., name="star")
sim.add(a=1., name="planet1")
sim.add(a=2., name="planet2")
sim.remove(name="planet1")