the arguments represent the Euler rotation angles. I just copy the explanation from TGeoMatrix.cxx:
The 30 as second argument in your example is not the rotation about Y, but about X.
This is the so-called X-axis convention (there are plenty others) and you can find detailed explanations at: mathworld.wolfram.com/EulerAngles.html
The difference related to this rule is just that the resulting matrix is the inverse, since in TGeo matrices always applies to local points/vectors to convert them to master reference system. On the other hand, having a second look I found out that the X-convention that I used is not quite consistent, so I applied the necessary changes that you can find in the CVS version.
Thank you for your reply. You are right about the axis used for the
second rotation, and now I see that the user’s guide also has the
same definition. I was confused from looking at the online
documentation for the TGeoRotation constructor at root.cern.ch/root/html310/TGeoRotation.html
So, I guess that needs to be fixed.
Thanks also for the pointer to the x-axis convention. I guess that I
am more used to the notation from the classic Goldstein textbook.
Plus, I seem to have had some plus/minus signs mixed up. I will take
another look at the rotations after upgrading ROOT.