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Name

mkcube - create a uniform cube of equal massive stars (the borg)

Synopsis

mkcube out=snapshot [parameter=value]

Description

mkcube generates a random realization of a cube. Coordinates in X, Y and Z are uniformly randomly distributed on a cube with given size. Velocities by default are zero, but can be drawn from an isotropic distribution with choosen dispersion.

As with most NEMO programs, the center of mass is (roughly, see zerocm=) at the origin, thus coordinates run from -size/2 to +size/2.

Parameters

The following parameters are recognized in order; they may be given in any order if the keyword is also given. Use --help to confirm this man page is up to date.
out=
Output file name, in snapshot(5NEMO) format. No default.
nbody=
Number of particles. [Default: 256].
size=
Size of cube. [Default: 1].
sigma=
Isotropic velocity dispersion. [Default: 0.0].
seed=
Random number seed [Default: 0].
zerocm=t|f
Center c.o.m. ? [Default: t].
headline=
Text headline for output Default: none.
nmodel=integer
Number of models to generate. All models will be different here. Although mostly meant for benchmarks, generating more then 1 model can be useful to process very large snapshots (that normally won’t fit in memory) in a serialized fashion. See also snapsplit. Most NEMO programs will only read the first snapshot. See also mkgrid nmodel= for a faster way to benchmark.
[Default: 1]

See Also

mkgrid(1NEMO) , mkplummer(1NEMO) , snapshot(5NEMO)

http://arxiv.org/abs/1206.3857 (The gravitational field of a cube, Chappel et al.)

Benchmark

The following benchmark creates a large nbody cube, is gridded in an image cube and converted to a fits file (the fits file is normally half the size of the ccd file, since the latter uses double precision): 


    nbody=10000000
    nx=128
    mkcube cube1 $nbody 4.0
    snapgrid cube1 cube1.ccd nx=$nx ny=$nx nz=$nx zvar=z zrange=-2:2
    ccdfits cube1.ccd cube1.fits

and with the following timings (user and system times reported) on a 512GB machine: 

nbody  nx   size  size       mkcube         snapgrid            ccdfits
1e7   128   547MB   16    0.59u   0.55s    1.15u   0.48s
1e7   256          131                     1.74u   0.54s
1e7   512         1048                     2.31u   1.15s       4.03u  0.81s
1e8   128   5.4G          6.55u   7.31s   11.62u   5.89s
      256                                 15.46u   6.17s
      512                                 21.51u   6.75s
     1024                                 41.23u  16.45s
     2048                                 65.91u  63.51s
1e9   128   54G          69.05u  81.46s    73.83u  53.74s
      256                                 79.05u  42.24s
      512                                 81.07u  39.53s
     1024          8GB                   103.28u  43.67s         74.26u 5.21s
     2048         64GB                   145.19u  85.29s          -failed-

Author

Peter Teuben

Update History


26-Aug-93    V1.0 Created    PJT
25-mar-2022    added benchmark    PJT

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