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snapstack - superimpose two N-body snapshots


snapstack in1=in_file1 in2=in_file2 out=out_file [parameter=value] ...


snapstack reads in two N-body systems and outputs one containing particles from both. It may be used to set up collisions by specifying offsets in position and velocity space.

If more than two snapshots need to be stacked, multiple runs of snapstack. would be needed, or snapadd(1NEMO) can be used.


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.
Input data will be read from these files, which must be in snapshot(5NEMO) format. Only the first frames are used. Default: required.
Output data will be written to out_file.
Relative position of first snapshot w.r.t. second. Default: 0.0,0.0,0.0.
Relative velocity of first snapshot w.r.t. second. Default: 0.0,0.0,0.0.
If true, translate to center of mass before output. Default: false.
Shift system1 or system2? If the final system is shifted with center of mass moved to the center, this option is not relevant anymore. Default: 1.
Text message prepended to out_file. Default: none.


The mkmh97 script uses a simple parameterized setup to set two systems in either a near head-on collision, or a circular orbit. For a near head-on collision, three positive parameters are given: r0, v0, rp, with
        deltar=$r0,$rp,0 deltav=-$v0,0,0
For a (near) circular orbit two parameters are given, r0, v0, where v0 < 0:
        deltar=$r0,0,0 deltav=0,$v0,0

Chris Mihos orbinit program (v1.1 31-July-2001) sets up two disks in an orbit:

 -mrat  : mass ratio M1/M2 [1.0]                           mrat
 -geom1 : theta, phi of TREEBI1 disk [0.0 0.0]         thetmod1,phimod1  

 -geom2 : theta, phi of TREEBI2 disk [0.0 0.0]          thetmod2,  phimod2
 -para  : parabolic orbit [false]                             dopara=T
 -a     : semimajor axis in model units [100.0]            a  (ainp=T, doellip=T)
 -e     : orbital eccentricity [1.0]                       e  (einp=T, doellip=T)
 -hyp   : hyperbolic orbit (enter vp/vp_para) [0.0]          vp   (dohyp=T)
 -tp    : peri time in model units [24]                      tp
 -rp    : peri distance in model units [2.5]                 rp    (rpinp=T)
 -orb   : write out keplerian orbit [false]                  dorb=T
 -init  : initialize new TREEBI [false]                      doinit=T
 -ndisk : number of particles in each disk [0]               ndisk1,ndisk2
 -rsort : only create files [false]
 a  = rp / (1-e)
 e  = 1 - rp/a
 rp = a * (1-e)
orbinit -mrat 8.0 -geom1 195.0 265.0 -geom2 150.0 100.0 -para -tp 24.0 -rp 1.0 -init

See Also

snapadd(1NEMO) , kep2kep(1NEMO) , snapshot(5NEMO)


Joshua E. Barnes


22-jan-89    V1.1 ???    JEB
20-jun-03    V1.2 using new get_snap/put_snap    PJT
5-aug-06    V2.0 added shift= and made zerocm=f default    PJT

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