[seqfan] Re: 3D version of A000938: 3-in-line inside the nXnXn cube
rhhardin at att.net
Sun May 23 18:46:22 CEST 2010
Build a huge logical expression for the relations among X bits
representing all tuples in the answer and count what fraction of the 2^X cases are true.
Some less than exponential complexity is needed, and a good fan-in to reuse common cases efficiently; which will depend
on the problem.
rhhardin at mindspring.com
rhhardin at att.net (either)
> From: Douglas McNeil <mcneil at hku.hk>
> To: Sequence Fanatics Discussion list <seqfan at list.seqfan.eu>
> Sent: Sun, May 23, 2010 11:57:09 AM
> Subject: [seqfan] Re: 3D version of A000938: 3-in-line inside the nXnXn cube
> On Sun, May 23, 2010 at 11:03 PM, Ron Hardin <
> ymailto="mailto:rhhardin at att.net"
> href="mailto:rhhardin at att.net">rhhardin at att.net> wrote:
> I've set
> up a data dump at
> > http://rhhardin.home.mindspring.com/current.txt
I'm curious how
> you're computing the numbers so efficiently. My first
thought was to
> fix a corner, iterate over all possible second cells,
and then extend along
> all multiples. Then translate the triples
through the cube, and finally
> impose the octahedral symmetry, but I'd
have to be careful about that.
> Then I thought of doing it recursively
(as already mentioned in the thread)
> and computing only the extra
lines introduced by the "next" cube layer.
> But the first way didn't
seem practical, and the second hurt my
Department of Earth Sciences
> of Hong
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