# Re: Reversal of Conway's Life Algorithm

Subject: Re: Reversal of Conway's Life Algorithm
From: Fred A Watkins (fwatkins@hyperlogic.com)
Date: Thu Jan 13 2000 - 07:52:02 MET

stevem@iea.com (Steve McGrew) wrote:

>On Mon, 10 Jan 2000 19:15:17 -0600, "Dathan"
><dathan_bennett@yahoo.com> wrote:
>
>> I could write one that would start at a "best guess" population
>>layout and modify squares on the grid that it would tag as "critical" until
>>it stumbled upon the right one. However, I would probably be better off
>>just starting a new science fair project at that point, because such an
>>implementation would be almost useless to my purposes. Perhaps I _should_
>>get a new project, but this one just intrigues me a lot. If anyone stumbles
>>across any information on the subject, _please_ post it here or mail it to
>>me.
>>
>>Dathan
>
> I think you can do better than to do a brute-force genetic
>approach. For example, if you started at one point on a pattern, you
>could determine all possible previous-generation pattern possibilities
>in the nearby region, and gradually branch out. You will probably
>find that there is a tree of possibilities, and that most of the
>did, indeed, work out that way, you could very likely find that the
>search is fairly fast.
>
>Steve

Well, there's no difference between a pattern that finally vanished last
round and no pattern at all. Suppose the current field is blank. What was
the previous state? *Any* pixel could have been on before. In fact, if I
remember the details of the algorithm, *all* pixels could have been
active on the previous round (assuming the playing field is infinite).
So the previous state is all, none, or a *large* number of possibilities
in between.

In short: the algorithm is not uniquely reversible. Not even close.

So, Dathan, I'd suggest you try something else.

Fred A Watkins
fwatkins@hyperlogic.SNIP_THIS_OUT.com

Decode email address to contact me.

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