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snapcenter - translate snapshot data to coordinates centered on subset
snapcenter in=snap-file out=snap-file [parameter=value]
snapcenter translates the phase-space data in 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.
following parameters are recognized; they may be given in any order.
- Input data is read from snap-file, which must be in snapshot format. No default.
- Output data is written to snap-file. No default.
- 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].
- 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].
- 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].
- Write output center of mass (COM) as a single
body with total mass and COM coordinates as computed from weight=. [Default:
- (1993) MNRAS 261, 497. 1993MNRAS.261..497S
Picard,A. and Johnston, H.M. - (1994)
Cruz., F et al. - (2002) Rev.Mex.de Astr.y Astr. 38, 225
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
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