NBodyProblem

This program contains a few integrators, able to compute more or less precisely the solution of an N-Body problem.

Program arguments

The program arguments should be :

nBodyProblem [options] initFile [outputFile]

The initFile contains the presets of the simultation, it has to be specified. The outputFile will contains the trajectories of the bodies, its default value is out.csv. If it already exists the program will continue the computation from the end of this file.

Program options

The program options are the following :

• --euler Uses the explicit Euler integrator
• -t or --taylor Uses a 4-order Taylor serie
• --symplectic4 Uses a 4-order symplectic integrator
• -s or --symplectic6 Uses a 6-order symplectic integrator
• -e or --energy Corrects the energy of the system
• -o or --overwrite The output file will be overwritten

The default integrator running is the classic 4-order Runge-Kutta method

Initialisation file format

The file containing the simulation informations should have the following format :

bodyNumber,computationStep,computationTime[,outputStepRatio,G]
x1,y1,z1,vx1,vy1,vz1,m1
...

Where outputStepRatio indicates the ratio between the outputed step number and the computed step number. One step out of this much will be recorded in the file. The default value of this is 100. G is the gravitational constant used, its default value is 1, adjust depending on the units used. These two arguments are then optional. Try to choose the units so the system dimensions are as close as possible to 10^0.

Trajectories file format

The output file will have the following format :

bodyNumber,stepNumber,maxPosition,maxSpeed
t,x1,y1,z1,vx1,vy1,vz1 ... ,xn,yn,zn,vxn,vyn,vzn
...

maxPosition and maxSpeed gives the maximum intensity of each vectors, it can be used to quickly determine the system dimensions

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Authors :

• Fabio d'ORTOLI-GALERNEAU