*snapmass(1NEMO)*
and *snapcenter(1NEMO)*
have to be used if for some reason
the user want finite mass particles and a perfectly centered set of particles.

Note this particle distribution is only useful for display, e.g. spiral structure
in a Longitude-Velocity diagram, and should not be integrated with programs
like *hackcode3(1NEMO)*
.

**out=***out_file*- The data are written
to this file in
*SnapShot(5NEMO)*format [no default]. **ndisk=***num_bodies*- Number
of disk particles [default:
**2048**] **potname=***potential_name*- name of the potential,
see $NEMO/obj/potential for the current repository. The user can supply
his own, see potential(5NEMO)
. [default:
**plummer**]. **potpars=***pot_pars*- Paramaters to the user supplied potential. The number of parameters depends on the potential supplied, the first parameter is reserved for a pattern speed in future implementation. [default: not supplied, parameters as defined by potential(5) ].
**potfile=***pot_file*- Data_file(s) to the user supplied potential. The number of files depends on the potential supplied. [default: not supplied, datafile(s) defined by potential(5) ].
**rmin=***min_disk_radius*- Inner cutoff
radius of test-particle disk. [Default:
**0.0**]. **rmax=***max_disk_radius*- Outer cutoff
radius of test-particle disk. [Default:
**1.0**]. **a=***ratio*- Ratio of maximum spiral
perturbation w.r.t. base disk. [default:
**1**]. **k=***inv_rad*- Wavenumber of the spiral
pattern, such that
**2.pi.k.r**is the phase of the spiral density maximum. Positive means trailing spiral pattern. (note that this is defined in term of**sign=**, see below) [default:**1**]. **w=***width*- Width of the spiral arm along a galactic
circle. Depending on the next keyword this width is either is degrees along
a galactic circle if that is to be constant, or in length units if the
width of the spiral is to be constant. [default:
**15**]. **angular=t|f**- Is the width
of the spiral defined in angular terms, in which case the physical real
width linearly increases with distance from the galactic center, or is
is constant as a function of radius. [default:
**t**, i.e. defined in angular terms]. **seed=***random_seed*- Use random number seed. A zero seed will generate
a system-time dependant seed. [default:
**0**]. **sign=-1|+1**- Sign of the angular moment vector. Positive means counter-clock wise rotation. Not
**sigma=***s1,s2,s3*- Velocity dispersion (isotropic) in the X-Y plane, plus optionally an offset and exponential dropoff: s = s1 + s2 * exp(-r/s3). Default: 0
**sigmator=**- The ratio of the tangential to radial velocity dispersion. By default 1, but if you need realistic values, our local solar neighbor measures about 0.5 but the best self-consistent (despite these models are NOT) estimate can be set by using the value -1, in which case 0.5*kappa/omega is used. Default: 1
**nmodel=***n_models*- Number of output models. [Default:
**1**]. **linear=t|f**- Should the spiral be linear
or logarithmic. Although spiral galaxies are mostly logarithmic, for historic
reasons the default here is linear. [Default:
**t**] **headline=***message*- Text headline for output file [default: not used].

% time mkspiral s000 1000000 nmodel=40Here is a sample on some 2002-class machines:

U-sparc IIi/440 MHz: 161.30u 42.59s 5:04.85 66.8% PentiumIV 2.2 GHz: 29.54u 10.68s 2:40.14 25.1% PentiumIV 2.4 GHz: 26.46u 10.14s 1:37.71 37.4% G5 2.0GHz: 28.400u 24.660s 1:05.41 81.1% (at no load of 0.0) 33.460u 44.950s 13:01.31 10.0% (at full load of 2.0) P4/1.6 GHz: 69.940u 18.470s 4:50.64 30.4% (laptop) P4/2.6 GHz + SATA 27.400u 16.320s 0:52.13 83.8% 0+0k 0+0io 300pf+0w (at no load of 0.0) 27.790u 20.020s 1:52.22 42.6% 0+0k 0+0io 300pf+0w sum: 79.35u 3.72s 2:17.64 60.3% P2400 tsf: 0.00u 7.59s 1:59.46 6.3% P2400 sum: 13.610u 4.130s 1:10.12 25.2% P2600/SATA tsf: 0.010u 7.800s 1:09.74 11.1% P2600/SATA sum: 13.334u 2.915s 0:57.67 28.1% P2800/SATA (Peter’s asus ) tsf: 0.003u 4.696s 0:44.36 10.5% P2800/SATA sum: 68.63u 22.34s 2:31.54 60.0% U440 tsf: 21.85u 30.73s 2:32.06 34.5% U440

13-mar-89V1.0 createdPJT 6-apr-89V1.1 seed=0 implementedPJT 7-apr-89V1.2 angular keyword introducedPJT 26-feb-93V1.4 new potential keywrdsPJT 16-sep-95V1.5 added nmodel=, sign= ; radii now randomPJT 26-may-02added benchmark data for >2GB filesPJT 3-aug-09V1.8 and documented forgotten stuffPJT 11-aug-09V1.9 added sigmator=PJT