On Thu, Mar 19, 2015 at 8:07 AM, Pierre <pierre.guil...@gmail.com> wrote:
> Hi,
>
> I have just realized this, and thought it would be helpful to know for
> anyone playing with Sage's Rubik's cube abilitites. Here it is:
>
> While the following 3 commands:
>
> sage: CubeGroup().move("U")
>
> and
>
> sage: CubeGroup().plot3d_cube("U")
>
> and
>
> sage: RubiksCube().move("U").show3d()
>
> all take the convention that U means "move the face U clockwise",
> unfortunately the command
>
> sage: RubiksCube().move("U")
>
> assumes that U means "move the face U counter-clockwise".
>
> So yes, doing foo= RubiksCube().move("U") and printing foo displays
> something that is not consistent with what you get when calling
> foo.show3d().
>
> I thought it was something to do with 3d plotting being left-handed in Sage
> or whatever, but no, foo.show() also gives the "right" answer. And the
> convention for what the permutation U is, taken by CubeGroup and given in
> Joyner's book, is just not the one appearing when you print foo.
>
> It seems that inverses are taken, since RubiksCube().move("R*U") displays
> something that corresponds to U^-1 * R^-1 (by which I mean U^-1 first, then
> R^-1).
>
> In a nutshell: the __str__ method in RubiksCube seems to be broken, somehow.
>
> This is all quite confusing !
>
I'm not sure, but I wonder if one describes a left action on a set and
the other describes the right action. Left actions vs right actions
are indeed confusing. However, some people insist on being lefties and
others insist on being righties, so Sage is merely being agnostic in
presenting both:-)
That's my guess but I could easily be wrong.
> best
> Pierre
>
>
>
>
>
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