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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 coordinates can be produced using
one=t.
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(5NEMO)
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 view the center of mass of a system without ac
atually 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
(notice snapcenterp(1NEMO)
does not compute the velocity centroid).
Here
is an example 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)
,
snapcenters(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)
Power et al (2003)
- 2003MNRAS.338...14P - shrinking sphere method, S2.5
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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