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snapspin - add Z-angular momentum or Z-axial outflow to an N-body snapshot
snapspin in=snap_in out=snap_out [parameters=values] ...
snapspin
adds angular momentum in the Z-direction to the particles of a snapshot
By default, all particles are given the same angular frequency (spin),
omega. A positive value means counterclockwise rotation, as seen from the
positive Z-axis. If potential and/or forces are present, they are corrected
with the usual coriolis term.
Optionally the spin is allowed vary as function
of radius, and interpolated from a tabulated rotation curve, V(r). However,
the potential and forces cannot be corrected in this case.
Instead of angular
momentum, the particles can also be given a Z-axial outflow (or inflow).
An outflow curve can optionally also be specified in tabular form, the
same way as for spin/rotation. Again, no corrections to potential and forces
are made in these cases.
Use snaprotate(1NEMO)
to transform to a different
spin-axis, and snapshift(1NEMO)
to a different center of rotation.
The
following parameters are reckognized in any order if the keyword is also
given:
- in=snap_in
- Input data is read from snap_in, which must be in standard
snapshot(5NEMO)
format [no default].
- out=snap_out
- Transformed data is written
to snap_out, which will also be in snapshot(5NEMO)
format [No default].
- omega=value
- The amount of spin (units: velocity per length). If the keyword
rotcur (see below) is used, the value of omega is ignored. [default:0].
- rotcur=r_v_table
- An ascii table(5NEMO)
with radii and velocities in columns 1 and 2 resp.
If a table is supplied, the value of omega above is ignored. Between r=0
and the first radius the rotation curve is linearly interpolated, outside
the last radius a Keplerian falloff is assumed, and overall interpolation
is done using cubic splines (see spline(3NEMO)
). Note: radii in the table
must be sorted. Default: none.
- sign=1|-1
- The sign of the input rotation curve
from r_v_table. Note: Although meant to be +1 or -1, it’s value is simply
multiplied with the value interpolated from the input rotation curve. It
can also be used in outflow mode, in which case -1 can be used for inflow.
[Default: 1].
- outflow=t|f
- A boolean flag used to change between spin and
outflow mode. By default spin is added to a snapshot (outflow=f).
- times=time-ranges
- Only snapshots with time values within times-ranges, which is of the form
ts[:te],..., will be copied. [default: all].
snaprotate(1NEMO)
, snapshot(5NEMO)
Peter Teuben
~/src/nbody/trans snapspin.c
18-Aug-87 Version 1.0: created PJT
9-Mar-88 V1.1: data history added PJT
6-jun-88 V1.2: new filestruct PJT
25-apr-89 V1.3: get/put_snap, omega bug removed PJT
22-jul-92 V1.5: added rotcur= and sign= PJT
1-feb-93 V1.7: fixed phi/acc PJT
28-apr-98 V2.0: added outflow= for Tony Wong PJT
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