ASTRO 498C: NEMO

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.

Startup

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

        nemo

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
  - ls > ls.out
  - ls | wc
- process control
  - hackcode out=big.out nbody=100000 tstop=10 >& big.log &
  - ^Z (control-Z: put in the background)
  - jobs
  - fg %1
  - ^C (control-C: kill process)
  - kill %1
user interface of NEMO programs (commandline arguments)
- system keywords
  - help=: get information on program keywords
  - yapp=: set the graphics output device; for PGPLOT e.g.:
    - /xs: X-windows
    - /ps: Postscript (default filename: pgplot.ps)
  - error=: bypass fatal errors
  - debug=: set debug level for output
- no need for keyword= if keywords are given positionally on the commandline.
- in=- or out=- mean standard input/output, which makes it very efficient to chain program through standard UNIX pipes:
```
        mkplummer - 100 | snapscale - - rscale=1,0.1,0.1 | snapplot -
        
```
- out=. means a bitbucket for data
get help on any NEMO program
- nemoman (X windows browsing program)
- man progname (standard unix program)
- progname help= (NEMO "inline" help")

Examples

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:

    2.00  8
    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
    snapshot in=cube.snap

or alternatively using a completely different package XGobi:

    snapprint cube.snap | xgobi

you can do some interactive 3D viewing (there are also programs for this in NEMO, e.g. snapxyz and xyzview)

Documentation

The 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 (A 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 alphabetically.
- programs (1NEMO).
- subroutines (3NEMO) .
- file formats (5NEMO) .
- administrativia (8NEMO) .
- local programs (lNEMO) .
- whatis manual database.
Books/Papers:
- "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" Sellwood J.A. (Ann. Rev. Astron. Astrophys. Vol. 25, pp. 151 1987).
- "Hierarchical N-body Methods" Hernquist, L. (Computer Physics Communications, Vol. 48, p. 107, 1988.)
- "The Numerical Solution of the N-body Problem" L. Greengard. (Comp. in Phys. pp. 142, mar/apr 1990.)

References

NEMO home page. This page
STARLAB ; Piet Hut, Steve McMillan and Jun Makino; you may find a local copy in $NEMO/usr/starlab .
TIPSY , an interactive X-windows based display package maintained by Neal Katz and Tom Quinn. Their HPCC project also maintains a software archive.
The IDL Astronomy User's Library has some routines to aid in plotting N-body systems.
Other interesting vizualization packages/programs:
- XGobi
- Dynamic Queries: Spotfire demo (cf. tabview in NEMO)

teuben@astro.umd.edu. 11-nov-97