nbodyzip

A lossy compressor of dark matter-only N-body simulation data

Installation and usage

To compile the source code,

g++ -std=c++17 -o nbodyzip main.cpp

To use nbodyzip,

./nbodyzip [input_format] [output_format] [input_file] [output_file]

The input/output format can be one of tipsy, posvel, and zip.

For example, to compress a pkdgrav3 snapshot, run

./nbodyzip tipsy zip snapshot.xxxxx snapshot.xxxxx.nz

To decompress, run

./nbodyzip zip tipsy snapshot.xxxxx.nz snapshot.xxxxx.2

Input/output formats

`tipsy`

nbodyzip supports tipsy files that contains only dark matter particles and the number of particles along each dimension should be a power of two.

`posvel`

is a binary format (system-dependent endianness) defined in nbodyzip. It contains a 32-byte header, an array of particle positions, and an array of particle velocities.

Header: scale factor (fp64), number of particles (ui64), particle mass (fp64), and softening length (fp64, in units of mean particle distance);
Positions: x₁, y₁, z₁, ..., x_n, y_n, z_n (ui32 numbers representing coordinates between 0 and 1)
Velocites: v_x1, v_y1, v_z1, ..., v_xn, v_yn, v_zn (fp32)

`zip`

is a binary format (system-dependent endianness) defined in nbodyzip that efficiently stores simulation data. For a 1024³ simulation, the absolute errors of x, y, and z coordinates are less than 2^-22, 2^-22, and 2^-21; the absolute error of v_i is 1.5×10^-5(1+(v_i/v_scale)), with v_scale being the rms of v_i.

njpipeorgan/nbodyzip