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Wrapping Up the Planets

© Adam Hughes

We have spent the last couple of months developing the planets problem as fodder for simulation. While this particular problem (planetary movement) undoubtedly forms the core of many real computational research projects, our goal was not to conduct any in-depth studies, but to become a little more familiar with the basics of scientific simulation. To this end, the planets scenario served as a good learning tool, and a quick summary of what we did is in order this week.

We started by representing our solar system with a set of planets and a sun, each of which we represented as a point charge (probably not a very good approximation in this case, something that may be addressed in the near future). From there we decided we needed to move our heavenly bodies, so we developed some equations of motion and some methods for solving those equations of motion. We also realized that the forces between bodies are really what drives a simulation, so we spent some time exploring the various interactions in our mock solar system.

Having established the basics of our system and the methods to be used to study it, we took a brief aside and thought about how these principles might best be applied if the system were larger than the several hundred particles we would probably model for a solar system. In particular, we found that the use of cutoffs and neighbor lists can greatly enhance the speed performance of a simulation while maintaining the integrity of the calculation. Also, we talked a little about periodic boundary conditions and how they add some realism to a simulation.

Having covered the elements necessary for simulation, we moved on to talk about what kinds of quantities can be calculated in a classical simulation such as our hypothetical planets study. We discovered that there are two basic types of quantities to be found : static, or time-independent, properties; and dynamic, or time-dependent, properties. Both are readily available from a typical simulation, and both can provide insight into the true nature of the system which we are studying.

All in all, the planets problems serves as a very good introductory system to begin exploring simulation. It's easier to relate concepts to something with which we are all familiar (the planets), and then we can begin to extrapolate to more abstract concepts if we desire.

Next week, we'll get back to surveying some of the more recent happenings in scientific computing.

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