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gadget - binary format for N-body snapshot files


gadget is the format used by Springel’s gadget(1NEMO) code, and several other packages and code know how to read and write such files. These are either gadget binary files (a 256 byte header, followed by a number of families of particles (stars, halo, gas, etc.).

There is also an HDF implementation

Some description in gadgetsnap(1NEMO) .

The gadget2 format is an extension of the gadget1 format, with extra headers for each block. The gadget3 format is .... probably

something we can’t handle yet



Since gadget binary files have the structure of a Fortran unformatted file, the unfio(1NEMO) program can display the top level structure, e.g. the following two commands are identical
unfio ICs/galaxy_bigeendian.dat swap=t
unfio ICs/galaxy_littleendian.dat
  ### nemo Debug Info: 1   256
  ### nemo Debug Info: 2   720000
  ### nemo Debug Info: 3   720000
  ### nemo Debug Info: 4   240000
whereas of course much more information can be seen with gadgetsnap:
gadgetsnap ICs/galaxy_littleendian.dat - | snapmstat -
  0 0:39999  = 40000 Mass= 0.00104634 TotMas= 41.8535 CumMas= 41.8535
  1 40000:59999 = 20000 Mass= 0.00023252 TotMas= 4.65039 CumMas= 46.5039
  # Found 2 species:
Or here an example to split the two galaxies:
gadgetsnap ICs/galaxy_littleendian.dat - | snapmask - - 0:19999,40000:49999
    | snapcenter - gal1
gadgetsnap ICs/galaxy_littleendian.dat - | snapmask - - 20000:39999,50000:59999
| snapcenter - gal2
and here a funny analysis, draw your own conclusions:
snaprect gal1 gal1r
snaprect gal2 gal2r
snapcmp gal1r gal2r
  # time  Min  Qlow Median Qhigh  Max   Mean Sigma
  # obs=r
  0   2.57303e-07 3.97679e-06 6.6571e-06 1.38556e-05 4.10978e-05  9.74949e-06 7.71154e-06

See Also

gadget(1NEMO) , gadgetsnap(1NEMO) , gadget2pcs(1NEMO) , gadget1t2(1NEMO) , snapshot(5NEMO) , unfio(1NEMO)


Peter Teuben

Update History

22-feb-2020    placeholder written     PJT

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