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prun - cosmological particle-mesh (AP3M) integration code


prun dir=run_directory [parameter=value]


prun is a cosmological particle code, with the aim to follow the evolution of a large number of interacting particles under Newtonian gravity. A unique aspect of this version is the adaptive nature of the P3M method. A max number of refinements of the mesh calculations can be set, to be able to follow the evolution at small scales when large degrees of clustering occur.

The equations of motion governing the evolution of the particle distribution in an expanding cosmological model are solved in comoving coordinates. A time-centered leapfrog integration is used.

The current NEMO implementation of prun 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.


The following parameters are recognized in any order if the keyword is also given:
working run directory. Must already exist yet (see pstart(1NEMO) ) Inside the working directory a ASCII parameter file, prun.dat will be created, which contains the input parameters for the 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.
run 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]
final step. Normally you want this to be a multiple of ipout= (see below). [75]
steps between data output. The first step is not output (since it already exists), but each multiple of ipout (called iout) is output. One file is created per data output. The filename is $datadir/rv$irun(%04d).$iout(%04d) [25]
steps between restart dump output. The filename is $datadir/rvdump.dat1. [4]
delta-p, the time step. The starting time of these cosmological simulations is always defined to be 1.0. [0.84].
Accuracy parameter, see also eq. (11.2) in Couchman (1994). [1.5].
initial softening. [0.6].
minimum softening allowed. Setting sftinit = sftmin >= 3.5 makes the code run in PM mode, which speeds up the code by several (13) factors. [0.03].
maximum pairwise force error (%). This also influences the efficiency of P3M and AP3M. Small errors require large mesh-force softenings and hence large chaining cells. This value must be in the range of 3 to 10%. [6.0].
maximum refinement level. By setting this to 0 no mesh refinements are done, and you can use this to estimate the time saving of the A3PM algorithm. (In the standard case this saves about 40% for the final steps) [4].
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/].
initial data file. By default it is derived from the one presumably created by pstart(1NEMO) , $datadir/rv$irun(%04d).0000. File must be in rvc(5NEMO) format.


The following experiment sets up initial condition using pstart(1NEMO) , integrates them using prun(1NEMO) , converts data to NEMO’s snapshot(5NEMO) format and plots the projected particle positions in a 2 by 2 panel using snapplot(1NEMO) :

        % pstart dir=run123 istart=123
        % prun dir=run123 irun=123
        % cat run123/data/rv* | rvcsnap - run123.snap
        % snapplot run123.snap xrange=1:33 yrange=1:33 nxy=2,2

Note on the third line that we can use a wildcard in the conversion pipe, because the the lexicographically order is also in time order.


On a Sparc 10-30 with the default parametrs
    pstart   64"
    prun   5938"

See Also

pstart(1NEMO) , snapcomove(1NEMO) , rvcsnap(1NEMO) , rvc(5NEMO)

‘‘Cosmological Simulations Using Particle-Mesh Methods’’, H. Couchman, Ch. 11 in: XXX ed. Benz et al. 1994.

‘‘XXX’’, H. Couchman, (1991) ApJLett 368, L23-26.




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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