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pstart - initialization routines for cosmological particle-mesh (AP3M)
pstart dir=run_directory [parameter=value]
sets up an initial distribution of particles in a cubic region for use
with the prun(1NEMO)
AP3M N-body integrator.
Particles can be randomly placed
within the computational cube or placed uniformly on a cubic lattice. In
the latter case the number of particles needs to be a perfect cube. On this
initial distribution, a low amplitude fluctuation spectrum is imposed.
A Zel’dovich potential is derived on the grid, which is differenced and
used to displace the particles.
The current NEMO implementation of pstart
is a wrapper program, with the usual nemo user interface. It creates a parameter
file and calls the fortran executable. In this way it also hides some of
the complexities of the fortran user interface. SH PARAMETERS The following
parameters are recognized in any order if the keyword is also given:
Hugh Couchman (fortran), Peter Teuben (C)
- working run directory. Must not exist yet. Inside the working directory an
ASCII parameter file, pstart.dat will be created, which contains the input
parameters for the chained program. This run directory will also contain
logfiles, and subdirectories where the data and Green’s functions are stored
(but see below to override). No default.
- start label. This is a non-negative
integer, not to exceed 9999, which is used as a ID label. Data and log filenames
are automatically derived from this label id. 
- number of particles
- mesh points per side. Must be a power or 2. .
used in potential calculations for initial conditions. [0.6].
- max force
error (%) [.0].
- Accuracy parameter, see also eq. (11.2) in Couchman
- initial particle distribution (0=uniform 1=random). For
a uniform particle distribution iru needs to be a perfect cube. .
- Random number seed 1. [-1001].
- Random number seed 2, phi_k [-10001].
- physical scaling of the box in Mpc (?) .
- amplitude applied
to input fourier modes. [0.0004].
- Name of the fortran derived pstartP
executable file, which can reside anywhere as long as the host OS can
resolve it’s location (e.g. under UNIX anywhere in the $path command search
- Directory to store Green’s functions. Can require
up to 5Mb. By default it is placed inside the working run directory (see
- Directory to store data file storage. Requires
about 6 Nobj words (normally 4 bytes/word) times the number of snapshots
(ipout/ipstop + 1) By default it is placed inside the working run directory
(see dir=) [data/].
xx-xxx-xx Fortran version prun HMPC
7-may-94 V1.0 NEMO wrapper written PJT
16-may-95 V1.1 new version from Couchman PJT
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