this is a presentation to the RECAS summer school on Science Gateways proposing the GADGET-2 application. GADGET2 is a smoothed-particle hydrodynamics simulation for astrophysical systems. We are proposing to develop a science gateway portlet for easy access and use of this powerful application

1. Overview of GADGET-2
Hydrodynamic Galactic
Simulations
Bruce Becker | bbecker@csir.co.za
Coordinator, SAGrid
Meraka Institute, CSIR

2. Bruce Becker: Coordinator, SAGrid | bbecker@csir.co.za | http://www.sagrid.ac.za
Outline
● What is GADGET and what does it do ?
● Application implementation and
dependencies
● Execution model
● Proposed development strategy
● Current situation

3. Bruce Becker: Coordinator, SAGrid | bbecker@csir.co.za | http://www.sagrid.ac.za
GADGET: what is it ?
http://www.mpa-garching.mpg.de/gadget/
● GAlaxies with Dark matter and Gas intEracT
● Cosmological N-body/Smoothed Particle Hydrodymanics
simulations (SPH)
● SPH:
●
Divides a fluid into discrete elements (particles)
● Have a typical length, over which properties of the
constituents are ”smothed”
● Smoothing length can be made adaptive, based on local
conditions
● particularly suited to astrophysics simulations at all scales.

4. Bruce Becker: Coordinator, SAGrid | bbecker@csir.co.za | http://www.sagrid.ac.za
GADGET: What is it good for ?
● Can be used for studies of isolated systems, or for simulations
that include the cosmological expansion of space, both with or
without periodic boundary conditions.
● In all these types of simulations, GADGET follows the evolution of
a self-gravitating collisionless N-body system, and allows gas
dynamics to be optionally included.
● Both the force computation and the time stepping of GADGET
are fully adaptive, with a dynamic range which is, in principle,
unlimited.
● Can be used to address a wide array of astrophysically interesting
problems, ranging from colliding and merging galaxies, to the
formation of large-scale structure in the Universe

5. Bruce Becker: Coordinator, SAGrid | bbecker@csir.co.za | http://www.sagrid.ac.za
GADGET: What is it good for ?
Galactic sphere
collissions
Cosmological galactic structure evolution
http://www.mpa-garching.mpg.de/galform/millennium

6. Bruce Becker: Coordinator, SAGrid | bbecker@csir.co.za | http://www.sagrid.ac.za
GADGET-2 : ”The Millenium Run”
”The Millennium Run used more than 10 billion particles to trace the
evolution of the matter distribution in a cubic region of the Universe
over 2 billion light-years on a side. It kept busy the principal
supercomputer at the Max Planck Society's Supercomputing
Centre in Garching, Germany for more than a month. By applying
sophisticated modelling techniques to the 25 TB of stored output,
Virgo scientists have been able to recreate evolutionary histories
both for the 20 million or so galaxies which populate this enormous
volume and for the supermassive black holes which occasionally
power quasars at their hearts. By comparing such simulated data to
large observational surveys, one can clarify the physical
processes underlying the buildup of real galaxies and black holes.”
- http://www.mpa-garching.mpg.de/galform/virgo/millennium/

7. Bruce Becker: Coordinator, SAGrid | bbecker@csir.co.za | http://www.sagrid.ac.za

8. Bruce Becker: Coordinator, SAGrid | bbecker@csir.co.za | http://www.sagrid.ac.za
GADGET – Research or Teaching ?
● GADGET is a very serious research
application, running on the most powerful
computers in the world.
● For serious research, run parameters need to
be properly validated...
● ...”But as a teaching tool I think this idea could
be great.”
- Prof. Romeel DavéSARChI Chair in
Cosmology, UWC/SAAO/AIMS

9. Bruce Becker: Coordinator, SAGrid | bbecker@csir.co.za | http://www.sagrid.ac.za
Application implementation and
dependencies
● GADGET-2 is written in ANSI-C, with MPI-
bindings
● Inherently parallel, but can also be executed on
single CPU serially (good for testing)
● Requires:
● GNU Science Libraries
● FFTW
● (optional) HDF5 library for I/O

10. Bruce Becker: Coordinator, SAGrid | bbecker@csir.co.za | http://www.sagrid.ac.za
Execution Model
● GADGET requires a set of initial conditions and a parameter
file to execute – mostly defined in Makefile
● Frequent recompilation necessary
● Typical workflow
1) Create initial condition file for specific problem with MUSIC*
2) Compile gadget for specific problem
3) Setup parameter input file
4) run the code and wait (monitor output log)
5) run analysis on the resulting data.

11. Bruce Becker: Coordinator, SAGrid | bbecker@csir.co.za | http://www.sagrid.ac.za
Execution Model
Create initial conditions with MUSIC
Sim.conf → MUSIC → ics.dat
Research question -
”what would I measure
if the following scenario
happened”
Define simulation parameters
My­sim.param
Run the simulation
Gadget2 My­sim.param

12. Bruce Becker: Coordinator, SAGrid | bbecker@csir.co.za | http://www.sagrid.ac.za
Portlet – Must Haves
● Required input:
● Makefile
● Parameters file
● Require two-step portlet
● Generate initial conditions
● Run Gadget Simulation
● GADGET recompilation happens on the fly
● All other dependencies deployed on the computing
infrastructure
● Can be obtained from Jenkins or CVMFS at the sites

13. Bruce Becker: Coordinator, SAGrid | bbecker@csir.co.za | http://www.sagrid.ac.za

14. Bruce Becker: Coordinator, SAGrid | bbecker@csir.co.za | http://www.sagrid.ac.za
Portlet – Nice to Haves
● Simple ”wizard” to generate IC and param files
● Parametric jobs (with certain parameter ranges)
● Snooping of output to see state of the job