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   Convert from the body axes to stability axes.
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   Form:
   b = BToS( alpha, opt )
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   ------
   Inputs
   ------
   alpha       (1,1) Angle of attack (rad)
   opt         (1,:) 'matrix' or 'quaternion'

   -------
   Outputs
   -------
   b           (3,3) Transformation matrix
               (4,1) Quaternion

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