The method that got me to this conclusion is a classic *just Google it* style, as follows. Looking at the original n-body example there's no useful documentation, but the [about section](http://benchmarksgame.alioth.debian.org/u32/performance.php?test=nbody#about) says that is uses a simple [symplectic integrator](http://en.wikipedia.org/wiki/Symplectic_integrator). The [first order example](http://en.wikipedia.org/wiki/Symplectic_integrator#A_first-order_example) is the [semi-implicit Euler method](http://en.wikipedia.org/wiki/Semi-implicit_Euler_method), which appears to match the code. ↩
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