I agree. Surely in the code one has started with a right action (say) and
has then decided to sometimes convert it to a left action using inverses.
However, some consistency would be good :-) After all, various pieces of
code seem to disagree on what U is...
On Thursday, March 19, 2015 at 3:32:18 PM UTC+1, David Joyner wrote:
>
> On Thu, Mar 19, 2015 at 8:07 AM, Pierre <pierre....@gmail.com
> <javascript:>> 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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