Gravity

A prototype library for n-body simulations. Written in Julia.

Usage Instructions

First, the Gravity.jl file needs to be included and the module imported.

julia> include("path/to/Gravity.jl")
julia> using .Gravity

The module provides Body for creating bodies (stars, planets, blackholes). At instantiation, bodies need a position, a velocity, and a mass. Natural units for the simulation are astronomical units, years, and solar masses.

julia> earth = Body("Earth", # A name for the body
                    [1, 0],  # Position
                    [0, 2π], # Velocity
                    3*10^-6) # Mass
julia> sun = Body("Sun", [0, 0], [0, 0], 1)

For a three dimensional simulation, the positions and velocities in Body definitions should be three dimensional.

In order to run the simulation, the bodies need to be added to a System.

julia> sol = System("Solar System")
julia> add_bodies!(sol, [sun, earth])

We can now calculate the orbits. In its arguments, calculate_orbits needs the system (sol) and a discretized domain for the integration of the equations of motion.

julia> time_step = 0.001
julia> total_time = 1
julia> orbits = calculate_orbits(solar, # System
                                 0:time_step:total_time, # Time domain
                                 verbose = true) # This will print status messages

Plotting and Animating

Plotting and animations are done using Plots.jl. Options for plot (provided by Plots.jl) can be specified into a dictionary

julia> plotargs = Dict(:title => Solar System,
                       :xlim => (-1.5, 1.5),
                       :xlabel => "x (AU)",
                       :ylim => (-1.5, 1.5),
                       :ylabel => "y (AU)",
                       :aspect_ratio => :equal)

and the orbits plotted with plot_orbits.

julia> plot_orbits(orbits, # the array obtained from `calculate_orbits`
                   plotargs = plotargs, # arguments for `plot`
                   verbose = true) # for status messages

For three dimensional plots, dim = 3 needs to be passed to plot_orbits.

julia> plot_orbits(orbits, dim = 3, plotargs = plotargs, verbose = true)

Animations can be created with animate_orbits.

julia> anim = animate_orbits(orbits,
                             dim = 3,    # for 3D plots
                             every = 30, # save a frame "every N iterations"
                             plotargs = plotargs,
                             verbose = true)

See the examples folder for more.