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# Quaternions concatenation is the sum of angles ? (2)

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3 replies to this topic

### #1hbdevelop1  Members

Posted 28 November 2012 - 08:46 AM

Hello,

With the two quaterions q1=q2=(cos theta/2, sin theta/2, 0, 0)
Does the product q1q2 yield a third quaternion q3 equals (cos theta, sin theta, 0, 0) ?

This is the result I am expecting to have from my quaternion class, but I don't have it.
My expectation is based on the fact that the concatenation of q1 and q2 will yield a quaternion representing both rotations. That means, for me, the sum of the angles each quaternion represents if the rotations are around the same vector.

So, does the product q1q2 yield a third quaternion q3 equal (cos theta, sin theta, 0, 0) ?
Or is there anything wrong with my assumption ?

### #2Álvaro  Members

Posted 28 November 2012 - 08:50 AM

### #3J. Evola's Apprentice  Members

Posted 28 November 2012 - 08:50 AM

In mathematical world - yes.
In programming world - not necessarily, because of floating point rounding errors.

### #4Brother Bob  Moderators

Posted 28 November 2012 - 08:58 AM