[J3] [EXTERNAL] [BULK] Re: Commutativity of co_reduce

[Van Snyder]

On Fri, 2024-10-25 at 12:43 +0000, Clune, Thomas L. (GSFC-6101) via J3
wrote:
> I note that although matrix multiply per se is not commutative in
> general, it is sometimes e.g. when one has matrices that describe
> rotations in N-space.
> I think that this is only true in 2 dimensions. 

You don't need to do a computation to verify that three-dimensional
rotations are not commutative. Just put a die on your table. Rotate it
90° about the vertical axis, then 90° about a horizontal axis, for
example the one perpendicular to your line of sight, and note which
pips are on each face. Restore it to its original orientation, rotate
it 90° about the same horizontal axis, then 90° about the vertical
axis, and note which pips are on each face.

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