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mkplummer - generates a snapshot according to a truncated Plummer model
itemptr mkplummer(nobj, mfrac, rfrac, seed, snap_time)
int nobj;
real mfrac;
real rfrac;
int seed;
real snap_time;
DescriptionMkplummer constructs a Plummer model, with a spatial or mass
cut-off, after which it performs a coordinate transformation to the center-of-mass
coordinate system. The model is constructed in VIRIAL units (M=G=-4E=1, with
E the total energy), and finite spatial extent which can be regulated by
specifying mfrac or rfrac or using their default values. The distribution
function of a Plummer model is spherically symmetric and isotropic, and
is a polytrope of index n = 5. See: S.J. Aarseth, M. Henon and R. Wielen (1974),
Astron. and Astrophys. 37, p. 183. Mkplummer returns a pointer to a new item
in the form of a snapshot which contains the Plummer model. The number of
particles is given by nobj. The mass fraction mfrac of the (infinitely
extended) Plummer model indicates at which point the model is cut off:
no particles are sprinkled in beyond the radius at which the cumulative
mass equals mfrac. Alternatively, rfrac can be used as a direct choice
of the cut-off radius. If mfrac = rfrac = 1.0 then particles will be sprinkled
in all over space. If mfrac < 1.0 or rfrac < 1.0 then each particle is constrained
to lie within both the radial and (cumulative) mass bound. For example,
if rfrac( mfrac ) > rfrac then rfrac is the limiting factor, but if rfrac(
mfrac ) < rfrac then mfrac limits the extent of the Plummer realization.
Note: specifying either value may have no effect if the default value
of the other parameter is still the limiting factor; Beware! The seed=
for the random number generator can have any positive value. A value seed
= 0 will be converted into a unique new value using UNIX’s clock time, in
seconds since once-upon-a-time-in-the-seventies. The time at which the snapshot
applies is indicated by snap_time.
See Alsomkplummer(1NEMO), mkuplummer(1NEMO),
mkuplummer(3NEMO). BugsAuthorPiet Hut Files
kirin:/usr/piet/clib/mkplummer.c
23-Apr-87 Version 1.0: created PIET
10-Jun-88 Version 1.1: created PIET