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Name

direct4 - simple N-body integrator for GRAPE-4 Pipelined N-body engine

Synopsis

direct4 in=in_file out=out_file [parameter=value]

Description

direct4 is a simple equal timestep direct N-body integrator that is used with the GRAPE-4 Pipelined N-body engine by compiling it with the grape I/O libraries.

With a special compile flag this program can also compute the forces on the front-end instead of the GRAPE4 board.

Parameters

The following parameters are recognized in any order if the keyword is also given:
in=
input file name, in standard snapshot(5NEMO) format. No default.
out=
output file name, in snapshot(5NEMO) format. No default.
dt=
integration timestep. [Default: 1/32]
tstop=
Stoptime [Default: 2.0]
dtout=
Output timestep of datadumps. [Default: 0.25]
dtlog=
Output timestep for the logfile. [Default: 0.25]
eps=
Standard softening length. All particles share the same gravitational softening length. [Default: 0.05]
pcmode=t|f
Add a Predictor-Corrector step to the leapfrog integrator. [Default: f]

Compilation

The original program source code (grape.c) could be compiled with many flags (-Dxxx) to target different hardware boards (GRAPE1, GRAPE2, GRAPE3, HARP3). Although this was a flexible solution to code maintenance, the current source code (direct4.c) is a severely trimmed version of the original for HARP3=1 and NOSHARE.

Here are the compilation options: (not some will be mutually exclusive of others):

    EXACT_CALCULATION    no GRAPE, use exact calculations on HOST 
    CHECK_GRAPE        compare GRAPE with exact HOST calculations

See Also

hackcode1(1NEMO) , nbody0(1NEMO) , snapshot(5NEMO) , atos(1NEMO) , stoa(1NEMO)

Files


usr/pjt/grape    direct4.c
[makino]    grape.c (original code, compilable for all boards)

Author

Jun Makino, Peter Teuben

Update History


16-sep-89    V1.0 Initial workbench version w/ exact force calculation    JM
17-May-97    V2.0 Simplified version for NEMO and GRAPE4    PJT


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