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mkdisk - create a uniform-density test disk in an external potential
mkdisk out=snapshot [parameters=values ...]
up a uniform ‘‘cold’’ disk of test particles with positive angular momentum,
i.e. rotating counter clockwise (but see sign= below) in the gravitational
potential of a user-supplied potential in potential(5NEMO)
an input snapshot can be given, in which case the positions are taken
from this input file.
for a test disk with more parameters:
the density, velocity and dispersion are specified by a table as function
The following parameters are recognized in any order
if the keyword is also given:
- The data are written to this
file in snapshot(5NEMO)
format . Currently the potential and total energy
are stored in the Potential and Aux slots of the snapshot. [no default].
- Number of bodies particles [default: 2048]
- name of the potential, see $NEMOOBJ/potential for the current object repository.
The user can supply his own, see potential(5NEMO)
. [no default].
- Paramaters to the user supplied potential. The number of parameters depends
on the potential supplied, the first parameter is reserved for the pattern
speed. [default: not supplied, parameters as defined by potential(5)
- Optional data file(s) to the user supplied potential. The number of files
depends on the potential supplied. [default: not supplied, or datafile(s)
defined by potential(5)
- Inner cutoff radius of test-particle
disk. [Default: 0].
- Outer cutoff radius of test-particle
disk. [Default: 1].
- Total mass of the disk. The default total
mass is 0, since this is a testdisk. Since there are a few programs that
will not like mass-less particles, this keyword can be used, or snapmass
will have to be used before further action is taken. [default: 0].
- The fraction that the local velocity dispersion has w.r.t. the local rotation
velocity. If a number is given, radial and tangential velocity are by default
taken to be the same, with no Z-velocities. If two numbers are given, the
first one is the radial dispersion, the second one the tangential (currently
wihtout any 2*Omega/Kappa correction), and the Z dispersion 0. Finally,
when 3 numbers are given, random motions in Z are also added. [Default:
- Use random number seed. If 0 is given, a random number
is generated from the time of the day. [default: 0].
- Sign of the
angular momentum. 1 means counter clockwise rotation in the XY-plane (in
case you were wondering, our galaxy has sign=-1). [Default: 1].
- Input file, in snapshot(5NEMO)
format, of which the positions are used
as initial conditions. [Default: not used]. *** lost the implementation
- Normally the particles are distributed randomly in phase,
but setting this to true, they will be regularly spread between 0 and TWO_PI.
- A constant radial velocity (>0 means outward motion) added
to all particles. Default: 0.
- If random motions are added (see
frac=), the energy of each particle will change. By setting energy=t the
energy is conserved and the "circular" speed will be reduced. This way the
guiding center for epicyclic orbits will also be conserved. Note that this
only applies to motion in XY. For stars with too much random motion (if
frac too high), the random number generator is run again to ensure conserving
the planar motion kinetic energy. Default: false.
- Use absolute value
of velocity dispersion instead of fractional. Default: f
for density dropoff, and circular velocity dropoff. Default: 0,0
- (deprecated) Fractional loss in circular streaming as z increased. Use z0_v
- Text headline for output file [default: not used].
xx-feb-87 coding, still debugging PJT
21-Apr-87 V1.0: coding seems OK PJT
28-Apr-87 V1.1: keyword manss= added PJT
8-feb-89 V2.0: new implementation using potential(5) PJT
12-may-90 V3.0: new keywords for potential(5) PJT
12-mar-91 V4.0: NEMO 2.x PJT
9-jul-91 corrected a few lies in the documentation PJT
22-oct-91 V4.1: added in= optional input file PJT
12-jun-92 V4.2: nbody= is now second parameter, lost in= PJT
5-may-03 V4.4: added random Z motions by using frac= PJT
8-may-03 V4.5: added energy= PJT
13-dec-2017 V4.9: abs,z0,vloss= added PJT
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