Ok, so now you want to know how to actually run the planetary dynamics simulations.

Let me first just remind you of the three main aspects of this project:

1. to understand the equations that govern the dynamics of the Solar System
   For this part of the project you will have to do some research into the mathematical equations that are used in describing planetary dynamics. You should be thinking about what equations you might need to actually write a computer code that simulates Solar System dynamics.

2. to understand numerical instabilities resulting from a bad choice of the timestep parameter. This type of numerical instability is due to approximations in converting the mathematical equations that govern the system into discrete equations used in the numerical scheme
   This part of the projects covers the numerical side of the project, as we convert the mathematical model that describes the physical system to a numerical system - the computer code. Here you will be experimenting with the timestepping part of the code - how long you need to run the simulations for, as well as what sized timestep you will need to take.

3. to experiment with the parameters (such as planetary mass, eccentricity and semi-major axis) to try and make a physically unstable system - and explain why the resulting system is - or is not - stable
   This part of the projects covers the physical model used to describe the system. Here you actually get to run some numerical experiments - but you should be thinking about what would make a planetary system physically (meaning really!) unstable. You should experiment with the masses, eccentricities and semi-major axes of the planets (and the number of planets) to better understand planetary dynamics.

You should be ok to get through the first two parts of the project by yourselves (though I can of course help out if you need it). I imagine that the third part, however, will be new to most of you. Let's have a look at the simulations, the timestepping and numerical instabilities in a bit of detail. You may also find this PowerPoint presentation (1.5M) on Numerical Simulations (from the Tools of Modern Astronomy unit) helpful.

For details of how to actually use the simulator and run your planetary dynamics jobs, see the How To page.
Don't forget to keep a record of your experiments!

The most difficult part for you will be knowing what values to enter for the various time paramters, including the integration timestep and output timestep parameters. The integration timestep is related to the numberical stability of your simulations so needs to be chosen carefully. You will understand its importance once you go through the equations of motion that govern planetary dyanmics. If you need help with this, just ask.

The simulator won't allow you to run really long jobs and in fact only allows you to have a maximum of 2000 datapoints in time. This mean that your total time, T_int, divided by the output time, dt_out, must not exceed 2000. And you don't want your data to be too 'course' either (which means that you don't record your output often enough). So you might have to do some restart ('continue from pervious simulation'). The best way to understand what all this means is by experimenting with the various time paramters and see what happens.

Now you should be ready to run your own experiments. Good luck!

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