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Name

orbint - integrating single stellar orbit

Synopsis

orbint in=orbit out=orbit [parameter=value]

Description

orbint will integrate a stellar orbit. It is currently implemented with a few simple constant-timestepping algorithms with minimal support for diagnostics and restart options. For fancy integrators see for example orbintv(1NEMO) or the newton0(1NEMO) family of orbit integrators.

Non-rotating potentials are also supported, but only with the rotation axis defined along the Z-axis.

Integrations backwards in time can be achieved by setting dt<0, since no stop time is given, but the number of steps is used to terminate the integration.

Parameters

The following parameters are recognized in order; they may be given in any order if the keyword is also given. Use --help to confirm this man page is up to date.
in=in-file
input file, in orbit(5NEMO) format [no default]
out=out-file
output file, will be in orbit(5NEMO) format [no default]
nsteps=number
number of integration steps [default: 10].
dt=time-step
time step (constant) to be taken. Negative values are allowed to achieve integrations backwards in time. [default: 0.1].
ndiag=number
number of timesteps when diagnostics are checked and output to stdout. [default: 10].
nsave=number
number of timesteps when data must be save to output orbit-file. Note that the program must have run to completion before the actual saved data are saved to the specified output file. [default: 1].
potname=name
name of file of potential(5NEMO) descriptor. If no name given, the potential name of the input orbit is used. [default: none].
potpars=par-list
List of parameters to the potential descriptor. The first parameter MUST be the pattern speed in the x-y plane. The remaining parameters are used by the _inipotential() routine in the potential descriptor. [default: none - use default from input orbit].
potfile=name
name of an optional datafile to the potential descriptor. This might be an N-body snapshot or list of spline fit coefficients etc. [default: none - use default from input orbit].
mode=int_mode
Specify the integration mode. Any one of euler, leapfrog, rk2, or rk4 can be given. [Default: rk4].
eta=
Relative error allowed in energy conservation. Integration is terminated if the relative error (|dE/E|) is too large. By default not used.
variable=t|f
Use variable timesteps? If so, the error control parameter eta= needs to be specified. Also note that not all integration methods support variable timesteps. Default: f.
tstop=
If given, this will override nsteps=. Default: not used.

Examples

The following example launches a particle from the Y axis (at y=1) in the X direction (speed 0.4) in a plummer potential. Although the 6D initial conditions are fully specified, so a potential (potname=) is not needed, it is tagged along with the orbit, such that the orbint integrator will use it. The integrated orbit is then passed on to a simple plotting program, which plots an X-Y view of this 2D orbit. 
mkorbit - x=0 y=1 z=0 vx=0.4 vy=0 vz=0 potname=plummer |\
     orbint - - nsteps=10000 dt=0.05 ndiag=1000 |\
     orbplot -
Using pattern speed = 0
pos: 0.000000 1.000000 0.000000  
vel: 0.400000 0.000000 0.000000  
etot: -0.627107
lz=-0.400000
Pattern speed=0
0.000000 0.080000 -0.707107     -0.6271067811865 -8.85195e-17
50.000000 0.118074 -0.745181     -0.6271067924302 1.79294e-08
100.050000 0.214977 -0.842084     -0.6271068023637 3.37697e-08
150.100000 0.214182 -0.841289     -0.6271068142254 5.26845e-08
200.150000 0.117347 -0.744454     -0.6271068268041 7.27429e-08
250.200000 0.080125 -0.707231     -0.6271068377636 9.02191e-08
300.250000 0.126220 -0.753327     -0.6271068490425 1.08205e-07
350.300000 0.222816 -0.849922     -0.6271068584659 1.23232e-07
400.350000 0.205165 -0.832271      -0.627106871307 1.43708e-07
450.400000 0.109993 -0.737100     -0.6271068833543 1.62919e-07
Energy conservation: 1.62919e-07
Read orbit with 10001 phase-points

See Also

mkorbit(1NEMO) , orblist(1NEMO) , orbintv(1NEMO) , epic5(1NEMO) , potential(5NEMO) , newton0(1NEMO) 
GALA: Galactic astronomy and gravitational dynamics (ascl:1707.006) - https://github.com/adrn/gala

Timing


With fpa on SUN 3/50 (~16Mhz) 1000 integration steps
potential=harmonic    1s
potential=plummer    1s
potential=bar83      3s
potential=hackforce    10s (100 bodies, standard Plummer model)
potential=hackforce    30s (500 bodies)
potential=hackforce    50s (2000 bodies)
potential=hackforce    80s (8000 bodies)

Author

Peter Teuben

Files


src/orbit/misc      orbint.c

History


xx-jul-87    V1.0: Created: simple Eulerian    PJT
2-May-88    V2.2: many changes + doc; leapfrog implemented    PJT
2-Jun-88    V2.3: new filestruct, code same       PJT
14-jun-91    V2.5: added variety of options, removed various bugs    PJT
26-mar-92    V2.5b: documented that rot.potentials are OK -       PJT
24-may-92    V2.6: default potential now taken from orbit    PJT
9-jun-92    V2.7: fixed rotating potential bug    PJT
19-apr-95    V3.1: various, rk4 is now default integrator    PJT
3-feb-98    V3.4: added eta= to control termination if errors bad     PJT
19-feb-03    examples...    PJT
10-feb-04    V4.0: started variable timestepping    PJT

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