https://github.com/shamazmazum/n-body-sim
N-body simulation (movement under the influence of gravitational forces).
https://github.com/shamazmazum/n-body-sim
nbody-sim opencl physics-simulation
Last synced: 3 months ago
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N-body simulation (movement under the influence of gravitational forces).
- Host: GitHub
- URL: https://github.com/shamazmazum/n-body-sim
- Owner: shamazmazum
- License: bsd-2-clause
- Created: 2019-09-15T06:46:58.000Z (almost 6 years ago)
- Default Branch: master
- Last Pushed: 2023-06-19T19:49:32.000Z (almost 2 years ago)
- Last Synced: 2025-02-09T10:11:18.393Z (4 months ago)
- Topics: nbody-sim, opencl, physics-simulation
- Language: C
- Size: 5.22 MB
- Stars: 0
- Watchers: 3
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
N-Body-Sim
=========
[](https://cirrus-ci.com/github/shamazmazum/n-body-sim)
**n-body-sim** is a simple program which simulates the movement of N bodies
under the influence of their gravitational forces in two dimensional space. It
uses simple O(n^2) algorithm executed on GPU, faster O(n*log n) will be
implemented later.
The gravitational force used in the program is:
$\vec{F} = G \frac{m_1 m_2}{({\left|\vec{r} \right|}^2 + \epsilon )^{3/2}} \vec{r}$
where ε=1 and G=100.
Usage:
```
n-body-sim -n nbodies [-o steps] [-i steps] [-d delta] [-s solver]
[--output-prefix prefix] [--no-update] position velocity
```
The flags mean following:
* `-n nbodies` Set the number of simulated bodies to `nbodies`. This is
automatically rounded to be a multiple of GPU working group size (see below).
* `-o steps` Write an output file each `steps` iteration. The output file is a
text file containing coordinates of each body, one coordinate per line. X and
Y coordinates are separated by space.
* `-i steps` Calculate motion invariants each `steps` iteration. Invariants
include total energy and angular momentum.
* `-d delta` A measure of time between two iterations. Smaller value will result
in more accurate computations. When `delta` is good enough, the invariants of
movement will change only insignificantly.
* `-s solver` A solver for the equation of movement. Three solvers are
supported: `euler`, `rk2` and `rk4`. `rk2` and `rk4` are 2nd- and 4th- order
Runge-Kutta methods. `euler` is the fastest among them and `rk4` is the most
accurate.
* `--output-prefix prefix` The names of output files will begin with this
prefix.
* `--no-update` Do not update input files on exit (see below).
The last two mandatory arguments are paths to files containing initial
coordinates and velocities of particles in the system. These two files must
contain exactly `nbodies` lines with X and Y components of a vector separated by
a space or many spaces. One set of these files is included in the `examples`
directory of this repository.
When the program receives `SIGINT` or `SIGTERM` signal (when you press `^C` or
`kill` it), it overwrites `position` and `velocity` files with updated values
unless `--no-update` option is specified.
Current restrictions: the number of bodies must be a multiple of maximal GPU
working group size (usually 256, see output of `clinfo`). Wrong number of bodies
is rounded to the biggest possible number which is less than the number
specified. A good number to start the simulation with is around 10k. Also all
bodies currently have the same mass (this is because clover has a limitation on
amount of memory I can use in kernel arguments with my GPU).
Output files can be converted to png (or jpeg) pictures with `gnuplot` and a
script like this:
```
#!/bin/sh
gnuplot << EOF
size = 45000
set terminal png size 1920,1080 enhanced font "Helvetica,20"
set xrange [-size: size]
set yrange [-size: size]
set output "$1.png"
plot "$1" with dots
EOF
```
Installation
-----------
You need these dependencies installed:
* OpenCL
* [program-map](https://github.com/shamazmazum/program-map) (a small helper for loading OpenCL programs)
* Cmake for building
The building procedure is following:
```
mkdir build
cd build
cmake ..
make
make install
```