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snapvirial - scale snapshots while retaining or setting virial ratio
snapvirial in=in_file out=out_file [parameter=value] ...
copies an N-body system from in to out, scaling particle qantities such
that the virial ratio is either retained or gets a specified value. For
a more manual rescale use snapscale(1NEMO)
The input snapshot must not
only contain masses and phase space information, but also potential, as
to make the rescaling computation a linear operation. Depending on accuracy
needed, a general algorithm as in hackforce(1NEMO)
can be used to add potentials
and forces to a snapshot.
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 file, in
format. Default: none.
- output file, also snapshot
format. If none supplied, the current virial ratio is reported, 1 being
the ideal virialized case.
- Scale the masses? [default: f].
- Scale the positions? [default: t].
- Scale the velocities? [default:
- Only snapshots with time values within times-ranges,
which is of the form ts[:te],..., will be scaled and copied. [default: all].
- virial=positive ratio
- Virial ratio (must be non-negative) to be obtained
- rescaling is done such that a virial ratio of |2T/W| is obtained. If no value
is given, the old virial ratio is retained [default: not used].
Scaling an already virialized Plummer sphere (see mkplummer(1NEMO)
the Faber-Jackson relation, one can also use snapscale(1NEMO)
to scale such
models, here with a massfraction a:
mkplummer plum1.dat 10000
snapscale plum1.dat plum2.dat mscale="$a" rscale="$a**0.5" vscale="$a**0.25"
It is considered an error when either the potential energy is positive
or the kinetic energy is negative. This usually requires the snapshot to
be in the center of mass frame. Use snapcenter(1NEMO)
if need be.
has no intelligence about the shape of the system, and hence does a simple
rescaling of the required quantities. It thus works quite well for spherical
12-March-89 V1.0: created PJT
6-apr-89 V1.1: added keywords 2t/w (bug?) PJT
11-aug-89 V1.2: mscale added and logic improved PJT
29-oct-90 V1.3: fixed decision bug PJT
11-nov-91 V1.3a: man page clarifications PJT
18-jul-2012 V2.0: reporting mode when out= left blank PJT
13-jun-2022 add snapscale example using Faber-Jackson PJT
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