2. Quickstart (Python)

2.1. Installation

To quickly get up and running, simply type into a terminal (if you installed REBOUND in a virtual environment, activate it first):

pip install reboundx

At this point you are done and can skip to the Quick Start Guide below.

For a more complete installation, i.e., if you want any of the following:

  • Source code

  • The example files so that you can modify them locally.

  • To also use the C version

First follow the installation instructions for the C version in Quickstart (C). Then, to install the Python version from this repository, navigate to the reboundx directory and (you’d also do this to install the Python version after modifying any of the C code):

pip install -e ./

2.2. Quick Start Guide

You always begin by setting up your REBOUND simulation like you normally would, e.g.

import rebound
sim = rebound.Simulation()

To use reboundx, we first import it, and then create a reboundx.Extras instance, passing it the simulation we want to attach it to:

import reboundx
rebx = reboundx.Extras(sim)

We then add the effect we are interested in. There are two types of effects, forces and operators. The easiest is to go to the Implemented Effects page, which lists all effects and links to a jupyter notebook example of how to set it up. For a deeper discussion, see Tamayo et al. 2019. Loading a force/operator returns an object of the appropriate type. For example, let’s add some mass loss to the star:

mm = rebx.load_operator("modify_mass")

Each effect will have different parameters to set, listed on the Implemented Effects page and the examples. Forces, operators and particles have a params attribute that works like a dictionary. For example, let’s add an exponential mass loss (i.e., negative) timescale to the star (index 0) of 1000 time units.

sim.particles[0].params["tau_mass"] = -1000

You can add as many modifications as you’d like in the same simulation. Simply add them:

gr = rebx.load_force("gr")
gr.params['c'] = 1.e4 # set speed of light

The units for the various parameters should always match the units you’re using for the rest of the simulation (see the examples). When you’re done setting up the modifications you want, you just run your REBOUND simulation like you normally would:


Probably the quickest way to get up and running is to modify an existing example for your effect. You can find links to the appropriate examples here: Implemented Effects, as well as details of each implementation and citations.