Files and Pipes

Overview

Teaching: 5 min
Exercises: 5 min

Questions

What kind of files does NEMO use

Objectives

File Types

Unix Pipes

NEMO stores most of its data in binary format. We have already see that the tsf program can display such data. These files are hierarchical, named, and type tagged to promote interoperability. Later in this episode we will see there are a few types (e.g. SnapShot, Orbit, Image). Here is a SnapShot:

$ mkplummer out=p10.dat nbody=10 seed=123
$ tsf in=p10.dat

but since the first two keywords are in order, it’s much easier to skip the keyword= portion for those. The seed= keyword is much further down the list, so we explicitly pass it with the keyword name:

$ mkplummer p10.dat 10 seed=123
$ tsf p10.dat

char Headline[28] "init_xrandom: seed used 123"
char History[43] "mkplummer p10.dat 10 seed=123 VERSION=3.0b"
set SnapShot
  set Parameters
    int Nobj 10 
    double Time 0.00000 
  tes
  set Particles
    int CoordSystem 66306 
    double Mass[10] 0.100000 0.100000 0.100000 0.100000 0.100000 
      0.100000 0.100000 0.100000 0.100000 0.100000 
    double PhaseSpace[10][2][3] -0.609486 -0.221687 -0.450963 
      -0.0766784 -0.209397 0.396561 4.80925 -0.486182 -1.52575 
      0.418474 0.117766 0.230193 0.545314 0.0795464 0.0632245 
      0.0867019 -0.109128 -0.282036 0.377209 -0.213318 -0.0118330 
      . . .
  tes
tes

but we can also use this in a Unix pipe

$ mkplummer - 10 seed=123 | tsf -

and it should give exactly the same output, since the same seed=123 was used.

Example Data Files

Here we give some examples of some file types we have or can generate in NEMO. We invite you to explore them.

Binary Tables

There are some binary tables to store a distribution function for initializing N-body realizations of certain model galaxies.

$ tsf $NEMODAT/k5isot.dat

Snapshot

We have already seen this one. They are used to store a snapshot of an N-body simulation.

$ mkplummer - 10 seed=123 | tsf -

Image

$ ccdgen - noise 1,0.1 | tsf -

Orbit

$ mkorbit - x=1 vy=1 potname=plummer | tsf -

this will just be a single point (initial conditions), but in general an Orbit will store many samples in time, much like a series of snapshots for an N-body simulation. This example also shows the use of a potential descriptor with the potname= keyword.

Key Points

File Types

Unix pipes

previous episode

An introduction to NEMO

lesson home