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Conway's game of Life, just because.

On 5/8/19 4:26 AM, Paul Moore wrote:
> On Wed, 8 May 2019 at 03:39, Richard Damon <Richard at> 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