Q2Eul:

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   Converts a quaternion to 3-2-1 Euler angles. 
   Uses the input e(1) for e(1) near the singularity.

   Since version 1.
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   Form:
   e = Q2Eul( q, e )
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   ------
   Inputs
   ------
   q		(4,1)  Quaternion
   e		(3,1)  Euler angles

   -------
   Outputs
   -------
   e		(3,1)  Euler angles

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Children:

Common: Quaternion/Q2Mat
Common: Transform/Mat2Eul