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Name

mkhomsph - make homogeneous sphere

Synopsis

mkhomsph out=snapshot [parameters=values ...]

Description

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.

Parameters

The following parameters are recognized in any order if the keyword is also given:
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. [Default: 1.2].
2t/w=ratio
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. [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].

Bugs

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.

See Also

snapmass(1NEMO) , snapcenter(1NEMO) , mkhom(1NEMO) , snapvirial(1NEMO)

Update History


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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