# Euler matrices in Mathematica? [duplicate]

I recently got confused by the Euler matrices (the rotation matrices about the Euler angles) given by Mathematica. They seem inconsistent with the reference I found.

So I am referring to Arfken, 7th. From page 140-141 we find,

We can see that by default Mathematica define the Euler matrices the same way as Arfken did: rotate the $x_3$ first then the $x_2'$ then the $x_3''$ again -- the (3,2,3) way in Mathematica. And both are rotated counterclockwise.

So when I put EulerMatrix[{$\alpha$, 0, 0},{3,2,3}] in Mathematica, I support to get the matrix $R_z(\alpha)$ in Arfken. And EulerMatrix[{0, $\beta$, 0},{3,2,3}] for $R_y(\beta)$, etc. But not, in Mathematica 11.0 I got:

So Mathematica gives the inverse matrices of those defined by Arfken. I am confident to the Arfken's results and can solve problems with them. But somehow Mathematica seems define the Euler matrices or rotation matrices in a different way. So if you want to use those rotation matrices in Mathematica, you end up with the opposite rotation as you expected from Arfken's rotation matrices. Does anyone have a idea about this?

• So basically Mathematica treats all the rotation transformation as active transformation while Arfken and maybe other math books define the Euler matrices as passive transformations. That's why we have inverse results here. – Andrew Sep 11 '17 at 17:18
• In either case, I would email support@wolfram.com and tell them about your confusion. The documentation can always be improved and (I think) feedback helps make that happen. – chuy Sep 11 '17 at 17:19
• FWIW: if you post-multiply a vector with these matrices, you'd get the effect expected in Arfken and other refs. – J. M.'s technical difficulties Sep 11 '17 at 18:23

• To use a very simple example: RotationMatrix[θ].{x, y} rotates {x, y} by θ anticlockwise, while {x, y}.RotationMatrix[θ] rotates {x, y} by θ clockwise, for positive θ. (The reverse happens for negative θ.) – J. M.'s technical difficulties Sep 12 '17 at 18:30