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snapcenter - translate snapshot data to coordinates centered on subset
of bodies
snapcenter in=snap-file out=snap-file [parameter=value]
...
snapcenter shifts the phase-space data from an input snapshot
file to a coordinate system centered on an arbitrary subset of bodies. More
precisely, real-valued weights are specified for each body, and used to
compute a weighted phase-space centroid, which becomes the new origin of
the coordinate system.
Alternatively a new snapshot with a single particle
of total mass and these new center-of-mass coordintes can be produced.
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.
- in=snap-file
- Input data is read from snap-file, which must
be in snapshot format. No default.
- out=snap-file
- Output data is written to
snap-file. No default.
- weight=expression
- The value of expression is used to
compute the centroid. expression is a real-valued C language expression over
the real values x, y, z, vx, vy, vz, phi, m, t, and the integer value i.
[Default 1].
- times=time-range
- Only data frames with time values within time-range,
which is of the form, eg, "1.0:1.5,2.5,3.0", will be translated. [Default: all].
- report=t|f
- Report the center of mass coordinates. These are 2*NDIM numbers,
position and velocity, of the new center of mass in the old coordinates.
If you want to use snapcenter in a pipe, you need to reset report=f, since
both standard output and filestruct output will get merged, and become
illegable for the next program in the pipe. [Default: f].
- one=t|f
- Write output
center of mass (COM) as a single body with total mass and COM coordinates
as computed from weight=. [Default: f].
To just see the center of
mass of a system without creating an output file:
% mkplummer - nbody=100 zerocm=f seed=123 | snapcenter - . report=t
0.073515 0.006338 0.068154 0.005858 0.014697 0.059333
mkplummer - nbody=100 zerocm=f seed=123 | snapcenterp - . report=t
0.058525 0.087385 0.099227
and to analyze a whole series:
% mkplummer - nbody=100 zerocm=f nmodel=100 seed=123 | snapcenter - . report=t
| tabstat - 1:6
npt: 100 100 100 100 100 100
min: -0.25276 -0.233932 -0.239581 -0.094354 -0.127564 -0.128537
max: 0.259662 0.297318 0.42111 0.099852 0.101441 0.088769
sum: -0.476577 0.634456 0.928364 0.272159 -0.074268 -0.074884
mean: -0.00476577 0.00634456 0.00928364 0.00272159 -0.00074268 -0.00074884
disp: 0.0997349 0.0970942 0.103345 0.0386814 0.045105 0.0440842
skew: 0.0784864 -0.189295 0.702539 0.0190448 -0.223761 -0.157901
kurt: -0.0980693 0.039727 2.47228 -0.22483 -0.0507929 -0.106209
min/sig: -2.48653 -2.47468 -2.40809 -2.50962 -2.81169 -2.89873
max/sig: 2.65131 2.99682 3.98496 2.51103 2.26546 2.03061
median: -0.0011355 0.0115855 0.010902 0.0022755 0.0001605 -0.002766
snapcenterp(1NEMO)
, bodytrans(3NEMO)
, hackdens(1NEMO)
, hackforce(1NEMO)
,
snapshot(5NEMO)
W.L.Sweatman - (1993) MNRAS 261, 497. 1993MNRAS.261..497S (n-body)
Picard,A. and Johnston, H.M. - (1994) A&A, 76. 1994A%26A...283...76P (observational)
Cruz., F et al. - (2002) Rev.Mex.de Astr.y Astr. 38, 225 (n-body)
Joshua
E. Barnes.
3-jul-87 Created ? Josh
26-aug-93 1.4 added tab= for displaying center (@Tokyo) Peter
29-nov-93 1.4 documented earlier report= (ala tab=) addition PJT
26-feb-97 1.6 added one= and changed default of report= PJT
12-aug-22 added cross-refs PJT
15-may-23 examples PJT
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