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pstart - initialization routines for cosmological particle-mesh (AP3M) code


pstart dir=run_directory [parameter=value]


pstart 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:

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. [9999]
number of particles [32768].
mesh points per side. Must be a power or 2. [32].
softening used in potential calculations for initial conditions. [0.6].
max force error (%) [.0].
Accuracy parameter, see also eq. (11.2) in Couchman (1994). [1.5].
initial particle distribution (0=uniform 1=random). For a uniform particle distribution iru needs to be a perfect cube. [0].
Random number seed 1. [-1001].
Random number seed 2, phi_k [-10001].
physical scaling of the box in Mpc (?) [80].
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 path) [pstart.exe].
Directory to store Green’s functions. Can require up to 5Mb. By default it is placed inside the working run directory (see dir=) [greenfn/].
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/].


See prun(1NEMO) .

See Also

prun(1NEMO) , rvc(5NEMO)




Hugh Couchman (fortran), Peter Teuben (C)

Update History

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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