Table of Contents

*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)*
.

**mkspiral** is also used in the standard benchmark as
to measure disk I/O speed on a file just over 2GB.

**out=***out_file*- The data are written to this file in
*SnapShot(5NEMO)*format [no default]. **nbody=***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**]. **mass=**- Total mass of the disk. [Default: 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**]. **headline=***message*- Text headline for output file [default: not used].
**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**] **test=***test-mode*- The mode for testing. test=0 gives the normal test disk; test=1 the 2D coordinates are uniform random (-1,1); test=2 the 2D coordinates are all set to 1.0; test=3 no initialization (everything 0) [0]

% 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% U440And here a more modern benchmark on a i7-8550U CPU processor with different modes:

% time mkspiral $out 1000000 nmodel=40 seed=123 test=$test $test $out cpu: 0 . 3.05u 1.09 i5-1135G7 0 . 4.15u 1.56 i5-10xxx 0 s0 6.21u 2.16s 0:08.38 full computation on a i7-8550U CPU 0 . 6.40u 0.69s 0:07.10 1 . 3.49u 0.68s 0:04.17 only using 4 xrandom’s calls 2 . 2.32u 0.71s 0:03.03 constant initialization 2 . 1.43u 0.68s 0:02.12 - same , but with better caching barebody.h 3 . 0.65u 0.56s 0:01.22 no initialization (using calloc)

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 24-oct-2020V1.10 added test=PJT