Gravity Tree is an iPhone application that visualizes a tree based gravity solver. It can be downloaded for free on Apple's AppStore. Several hundred particles in a box with periodic boundary conditions are simulated and displayed in real time on the iPhone. This kind of simulation can be used to model the formation of planetesimals. Planetesimals are the building blocks of planets in the early solar system. Because of self-gravity planetesimals can clump and eventually form planets. However, to model the physical processes realistically, one has to use many more particles than the iPhone can handle.
Exactly the same simulation also runs on supercomputing facilities. The code is fully parallelized using the pthreads library (for shared memory systems) and MPI (for large scale computing clusters). It has been successfully tested with millions of particles.
The original idea of a tree code was presented in a nature paper by J. Barnes and P. Hut (Nature, 324(4):446-449, December 1986). A recent scientific publication describing some details of this particular code will be available for free on this site once it has been accepted by the journal.
Hanno Rein 2009
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hr260 -at- cam.ac.uk