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## 5.5.1 Initializing

There are a few programs with which orbits can be initialized:

• mkorbit is the most straightforward program. You can give simply give it all 6 phase space coordinates, and an orbit file consisting of this one point is generated. It is also possible to give the potential in which the particle is to move, and 5 phase space coordinates plus the energy, or even 4 phase space coordinates and the energy plus the total angular momentum or angular momentum along the Z axis (for axisymmetric systems).

Let's start with an example of creating a simple orbit by itself with no associated potential.

```% mkorbit out=orb1 x=1 y=0 z=0 vx=0 vy=0.2 vz=0
### Warning [mkorbit]: Potential potname= not used; set etot=0.0
pos: 1.000000 0.000000 0.000000
vel: 0.000000 0.200000 0.000000
etot: 0.000000
lz=0.200000

% tsf orb1
char History "mkorbit out=orb1 x=1 y=0 z=0 vx=0 vy=0.2 vz=0 VERSION
=3.2b"
set Orbit
set Parameters
int Ndim 03
double Mass 1.00000
double IOM 0.00000 0.200000 0.00000
int Nsteps 01
tes
set Potential
tes
set Path
double TimePath 0.00000
double PhasePath 1.00000 0.00000 0.00000 0.00000 0.200000
0.00000
tes
tes
```

• perorb is a program that for given initial conditions (similar to the ones described in mkorbit above) attempts to calculate periodic orbits in that potential. The output file will be a file with one (or more) orbits. This is a bit of an advanced program, and will not be covered here.

• stoo is a program that can take a particle position from a snapshot, and turn it into an orbit. For example, sampling some initial conditions from the positions of stars in a Plummer sphere, we could use the following small C-shell code to find some statistical properties of this selected set of orbits5.13

```    mkplummer out=p100 nbody=p100
foreach i (`nemoinp 0:100:10`)
stoo in=p100 out=orb\$i ibody=\$i
orbint orb\$i orb\$i.out 10000 0.01 10000 potname=plummer
orbstat orb\$i.out
end
```

The reverse program, otos turns an orbit into a snapshot, and may come in handy since the snapshot package has far more advanced analysis programs.     Next: 5.5.2 Integration Up: 5.5 Orbits Previous: 5.5 Orbits   Contents   Index
(c) Peter Teuben