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mkhomsph - make homogeneous sphere
mkhomsph out=snapshot [parameters=values
...]
mkhomsph creates a perfectly cold homogeneouss phere with
unity mass. Options exist to add random velocities and use a power density
law.
Models are not stable of course, but fun to play with or to study collapse
and violent relaxtion. More serious homogeneous models can be found in mkhom(1NEMO)
.
Friedman & Polyachenko (1986?, Part I) discuss how to make equilibrium models.
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.
- out=out_file
- The data are written to this
file in SnapShot(5NEMO)
format [no default].
- nbody=num_bodies
- Number of
stars in sphere [default: 2048]
- rmin=min_radius
- Inner cutoff radius of
the sphere. [Default: 0.0].
- rmax=max_radius
- Outer cutoff radius of the sphere.
The default values of rmin=0 and rmax=1.2 give a virial radius of 1.0 [Default:
1.2].
- 2t/w=
- Virial ratio which measures deviation from virial equilibrium
(two times the ratio of kinetic to potential energy, 2t/w must be positive).
Only accurate for a homogenous sphere (power=0 and rmin=0). See also vmax=
for an alternate means to specify scaling velocities. [default: 0].
- vmax=vmax
- Maximum of isotropic velocities. No scaling as function of radius is applied.
[default: 0].
- power=p
- Power law exponent of the density as function of
radius, Density rho = r^{-p}, thus centrally concentrated models have p >
0 . Values of p > 3 are illegal. [default: 0].
- seed=random_seed
- Use random
number seed. Non-positive have special meaning. [default: 0].
- zerocm=t|f
- Center
coordinates on center of mass after generation? [default: t].
- headline=message
- Text headline for output file [default: not used].
When shells are
created (non-zero rmin) the calculation of ’virial equilibrium’ velocity dispersions
is not correct anymore. See snapvirial(1NEMO)
for a slightly better approach.
mkvh60(1NEMO)
, snapmass(1NEMO)
, snapcenter(1NEMO)
, mkhom(1NEMO)
,
snapvirial(1NEMO)
20-mar-89 V1.0 created PJT
28-mar-89 V1.1 keyword ’rmin’ added PJT
5-apr-89 V1.2 keyword 2t/w implemented when rmin=0 PJT
6-apr-89 V1.3 keyword zerocm added PJT
20-may-97 V1.4 added vmax=, power= PJT
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