What is NEMO?
NEMO is an extendible Stellar Dynamics Toolbox. It has various
programs to create, integrate, analyze and visualize N-body and SPH like
systems. In addition there are various tools to operate on images,
tables and orbits, including FITS files to export/import to/from other
astronomical data reduction packages.
If you add the following command to you .cshrc file:
alias nemo 'source /local/rc/nemo.csh'
you can load NEMO into your environment by issuing the command
each time when you have started a new shell (or opened a new window).
To get the most out of NEMO make sure you understand:
- some basic unix shell operations
- X-windows, unix commands (ls, cp, mv)
- command line editing with the t-shell (tcsh vs. csh)
- redirecting input/output to/from files or other processes
- process control
- hackcode out=big.out nbody=100000 tstop=10 >& big.log &
- ^Z (control-Z: put in the background)
- fg %1
- ^C (control-C: kill process)
- kill %1
- user interface of NEMO programs (commandline arguments)
- get help on any NEMO program
- nemoman (X windows browsing program)
- man progname (standard unix program)
- progname help= (NEMO "inline" help")
Here is the example that was discussed in class.
Conversion of an Ascii table output file:
Make sure the tabular output of your N-body integrator is a set of snapshots,
where each snapshot is labeled with the time and the number of bodies
in that snapshot, followed by all the particle positions and velocities,
one on each line. Here is an example of 8 particles, at rest at the edges
of a cube of size 1, at snapshot time 2.00:
0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 1.0 0.0 0.0 0.0
0.0 1.0 0.0 0.0 0.0 0.0
0.0 1.0 1.0 0.0 0.0 0.0
1.0 0.0 0.0 0.0 0.0 0.0
1.0 0.0 1.0 0.0 0.0 0.0
1.0 1.0 0.0 0.0 0.0 0.0
1.0 1.0 1.0 0.0 0.0 0.0
The following NEMO commands would convert and display this data:
tabtos in=cube.tab out=cube.snap header=time,nbody block1=pos,vel
or alternatively using a completely different package
snapprint cube.snap | xgobi
you can do some interactive 3D viewing (there are also programs
for this in NEMO, e.g. snapxyz and xyzview)
Users and Programmers Guide is
an extensive (150 pages) manual. It's four major parts give
a general introduction, a cookbook with many examples, a
programmers guide and an appendix with many reference sections
postscript version is also available).
- Unix manual pages:
Good starting points are the manual pages
programs(8NEMO), which lists
programs thematically, and
index(1NEMO), which lists them
- "Computer Simulation Using Particles",
R. W. Hockney and J. W. Eastwood
(Adam Hilger; Bristol and Philadelphia; 1988)
- "Galactic Dynamics", Section 2.8 (pp 90-99)
Binney, J. and Tremaine, S.
(Princeton U. Press; Princeton; 1987)
- "The Art of N-body Building"
(Ann. Rev. Astron. Astrophys. Vol. 25, pp. 151 1987).
- "Hierarchical N-body Methods"
(Computer Physics Communications, Vol. 48, p. 107, 1988.)
- "The Numerical Solution of the N-body Problem"
(Comp. in Phys. pp. 142, mar/apr 1990.)
- NEMO home page. This
- STARLAB ;
Piet Hut, Steve McMillan and Jun Makino;
you may find a local
copy in $NEMO/usr/starlab .
an interactive X-windows based display package maintained by
Neal Katz and Tom Quinn. Their
also maintains a
Amara Graps's N-body/Particle simulation methods home page.
(This also includes a nice
summary from a sci.math.num-analysis newsgroup
discussion on N-body/Particle simulation numerical schemes.
IDL Astronomy User's Library has some routines to aid in
plotting N-body systems.
- Other interesting vizualization packages/programs: