Message #1048

From: Melinda Green <>
Subject: Re: [MC4D] Re: definition of a twist
Date: Mon, 19 Jul 2010 13:11:59 -0700


I know it’s been discussed too but I’ll just give my current opinion
which is that I like the idea of defining a twist as any combination of
currently supported twists on a single face that can be reduced to a
single one with a single slice mask. So a twist with one slice mask
followed by the same twist with a different mask should only count as a
single twist and represented in the log file with their combined mask.
Likewise three 90 degree twists should only count as one -90 degree
twist. And of course any combination that leaves the puzzle unchanged
shouldn’t count at all. I currently cancel pairs of twists that are the
inverse of each other, so long as they don’t cross macro boundaries. I’d
love to support more such cases.

The one case that I’m not currently ready to accept are combinations of
face twists that can be represented by a single transformation but which
are not reachable by a single existing twist. I’m talking about moves
like double 90 degree twists. At first blush that seems reasonable to
represent as an atomic move but look at the Onehundredagonal Duoprism.
It’s not at all clear to me that 37 single twists around the cylinder
should count as a single twist. maybe, maybe not.

Even though these sorts of changes will affect the twist counts of
previous solutions, there is the possibility of adding more twist
compression logic to MC4D or to a standalone program that will factor
out any redundancies so that comparisons will always be reasonably fair.
At the moment I don’t have plans to do any of this work but I think it’s
great to have these discussions in the hope that we can come up with the
prefect definitions to base future work on.


matthewsheerin wrote:
> […] I feel that it’s worth mentioning the old problem in MC4D. A face can be moved to most its possible positions in one move, but the three positions reached by two 90 degree twists require two moves. I’m sure it has been discussed before but a quick look didn’t find it.