Re: Reversal of Conway's Life Algorithm


Subject: Re: Reversal of Conway's Life Algorithm
From: dale (djohnson@v-wave.com)
Date: Mon Jan 10 2000 - 09:36:51 MET


>
> Actually, I'm only planning on running it back a few iterations, so size
of
> the search tree wouldn't be too much of a problem, or shouldn't be. After
> all, I could just divide a large grid into a bunch of smaller ones for the
> original search. The code to decide that the values of a certain area's
> squares is unaffected by the values of far-off squares should be fairly
> simple to write.
>

if your grid is 4 x 4, and at time T, your grid should be 6 x 6 at time
T-1, 8 x 8 at time T-2, and 10 x 10 at time T-3 in order to eliminate
border effects. your tree would have the 4 x 4 matrix as its root,
then branch to "n" 6 x 6 trees. To figure out time T-1, you more
or less have to search through 2^(6x6), 68 trillion possible boards
which may have produced the 4 x 4 board of interest. when you
locate those boards (perhaps 20 or 30), they are the next level
of your tree. you then have to search through 2^(8x8),
10^19 possible 8 x 8 boards which may have produced
your 6 x 6 boards, and compare against the 20 or 30 in
your previous set. This may be larger, there may be 100 or so
per branch, forming the third level of the tree.

that is the brute force method. if you know more about what you're
looking for maybe there are shortcuts. keep posting!

Dale.

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