Copyright(c) 2015 Kevin Arthur Schiff Croker GPL v2
This code implements an extension of the N-body code GADGET-2 by Volker Springel so as to enable computation with D distinct interacting gravitational species.
To use the code, one should first be familiar with GADGET-2, can be found here:
http://www.mpa-garching.mpg.de/gadget/
The contents of this repository are sufficient to GNU make:
- cd to the repo directory
- adjust Makefile for your system
For the included example, type:
cp Makefile.reference Makefile make
If one wishes the documentation and test files included with GADGET-2, one may download from the above URL and then replace the contents of the Gadget2/ subdirectory with the contents of this repository.
(Note that the included Makefile.reference works on modern Ubuntu systems, and with the included Galaxy collision initial condition from GADGET-2, modified so that particle types are distributed evenly across gravitation)
Gadget-2.0.7-ngravs is configured identically to GADGET-2. The following are new and mandatory configuration file options:
GravityGas [int]
GravityHalo [int]
GravityDisk [int]
GravityBulge [int]
GravityStars [int]
GravityBndry [int]
Here [int] will be any integer in [0,5] < N_GRAVS (as defined in Makefile) and specifies the gravitational interaction to be used by that particular GADGET-2 particle type.
To use ngravs for your particular model, modify the ngravs.c and ngravs.h files. Comments in the C file are quite verbose and there are two completely functional examples used to test the code, one may follow them as necessary.
(Note that the included Configuration.reference will run with the included modified Galaxy collision initial condition from GADGET-2)
For example, to run the included Galaxy Collision initial condition, type:
mpirun -n [int] ./Gadget2 Configuration.reference
Note that the included GalaxyCollision.IC file uses little endian encoding (like x86 platform). If you require big endian encoding, please use the analogous file from the original GADGET-2 code package.
accel.c: Driver routine to carry out force computation
allocate.c: Routines for allocating particle and tree storage
allvars.c: Provides instances of all global variables
begrun.c: Initial set-up of a simulation run
density.c: SPH density computation and smoothing length determination
domain.c: Code for domain decomposition
driftfac.c: Computes look-up tables for prefactors in cosmological integrations
endrun.c: Terminates run upon severe errors
forcetree.c: Gravitational tree code
global.c: Global energy computation
gravtree.c: Main driver routines for gravitational (short-range) force computation
gravtree_forcetest.c: Routines for direct summation forces
hydra.c: Computation of SPH forces and rate of entropy generation
init.c: Code for initialisation of a simulation from initial conditions
io.c: Routines for producing a snapshot file on disk
longrange.c: Driver routines for computation of long-range gravitational PM force
main.c: Start of the program
ngb.c: Neighbour search by means of the tree
ngravs.c: defines gravitational force laws for real space, k, and lattice sums
ngravs_core.c: defines ngravs treepm computations and other model-independent code
peano.c: Routines to compute a Peano-Hilbert order
pm_nonperiodic.c: Code for non-periodic FFT to compute long-range PM force
pm_periodic.c: Routines for periodic PM-force computation
potential.c: Computation of the gravitational potential of particles
predict.c: Drift particles by a small time interval
read_ic.c: Read initial conditions in one of the supported file formats
restart.c: Code for reading and writing restart files
run.c: Iterates over timesteps, main loop
system.c: Miscellaneous routines, e.g. elapsed time measurements
timestep.c: Routines for ‘kicking’ particles and assigning new timesteps
allvars.h: Declares global variables
ngravs.h: Contains ngravs specific prototypes
proto.h: This file contains all function prototypes of the code (non-ngravs)
tags.h: Declares various tags for labelling MPI messages (non-ngravs). Defines how ngravs
tags are determined from the pre-existing ones
TreePM in non-periodic settings has been disabled, so there are no "zoom" simulations at present. The transition computation has been correctly implemented (this was an error in the first release).
New Makefile options are detailed as well! -k@Tartu 2/10/16
To see how the extension works, as well as for some annotation on how the original Gadget-2 algorithms operate, I have interspersed various dated comments with 'KC MM/DD/YY' into the source files wherever I have made changes to the original source. Sometimes, these comments are quite explicit and reference technical works justifying the origin of a computation. I leave them in so that someone might easily check that what I have done is indeed correct (though it certainly seems to be the case...)
Regions in the code marked with XXX may be bugs. At present, there are only two sitting in pm_nonperiodic.c. Here, it seemed that a bunch of code was needlessly repeated, and so I commented it out with an explanation, but tagged it as possibly suspect.
Regions in the code marked with PPP may be amenable to performance improvements. If you'll note, Volker was quite rigorous in eschewing divisions, making references to the same variables spatially proximate in the code, unrolling loops, etc. It turns out that these things matter, see the comments to get an idea of some of the performance gains!
I hope ngravs is useful for investigation of your wild gravitation models! If you use it, please cite the relevant code paper, submitted to Comput. Phys. Commun. (Computer Physics Communications).
Word! -k@Manoa 2/7/15 -k@Pitt 6/4/15
Acknowledgments:
This material is based upon work supported by the National Science Foundation under Grant Number 1415111. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.