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On 5/8/19 4:26 AM, Paul Moore wrote: > On Wed, 8 May 2019 at 03:39, Richard Damon <Richard at damon-family.org> wrote: >> My experience is that the wrap around is common, as otherwise the hard >> edge causes a discontinuity in the rules at the edge, so any pattern >> that reaches the edge no longer has a valid result. The torus effect >> still perturbs the result, but that perturbation is effectively that the >> universe was tiled with an infinite grid of the starting pattern, so >> represents a possible universe. > In my experience, "simple" implementations that use a fixed array > often wrap around because the inaccuracies (compared to the correct > infinite-area result) are less disruptive for simple examples. But > more full-featured implementations that I've seen don't have a fixed > size. I assume they don't use a simple array as their data model, but > rather use something more complex, probably something that's O(number > of live cells) rather than something that's O(maximum co-ordinate > value ** 2). > > Paul > An implementation that creates an infinite grid to work on doesn't need to worry about what happens on the 'edge' as there isn't one. I suspect an implementation that makes an effectively infinite grid might not either, though may include code to try and keep the pattern roughly 'centered' to keep away from the dragons at the edge. If, like likely with a 'high efficiency' language with fixed sized integers, the coordinates wrap around (max_int + 1 => min_int) then it naturally still is a torus, though processing that case may add complexity to keep the computation of a typical cell O(1). You might end up with numbers becoming floating point, where some_big_number +1 -> the same some_big_number that would lead to issues with the stability of the data structure, so maybe some hard size limit is imposed to prevent that. So it comes to that if there is an edge that you might see, the normal processing is to wrap to make the edge less disruptive. If you aren't apt to see the edge, then it really doesn't matter how it behaves (sort of like how people aren't concerned about the Y10k issue) -- Richard Damon

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