QFrenet:

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   Generate the quaternion that transforms from the ECI to the Frenet frame.

   The coordinates of the Frenet frame are defined as:
        x: Along velocity
        z: Orbit-normal, or cross-track
        y: Bi-Normal axis, Completes RHS (Zenith for circular orbits)

   The relative position vector in the Frenet frame can be computed as:

   rF = QForm( qEF, drE );

   where dr is the relative position vector in the ECI frame. Or you may obtain 
   the transformation matrix, mEF, as the second output. In this case, use:

   rF = mEF*drE;

   Since version 7.
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   Usages:
   qEF       = QFrenet( rE, vE );
   [qEF,mEF] = QFrenet( rE, vE );
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   ------
   Inputs
   ------
   rE              (3,1) ECI frame position
   vE              (3,1) ECI frame velocity

   -------
   Outputs
   -------
   qEF             (4,1) ECI to Frenet quaternion
   mEF             (4,1) ECI to Frenet transformation matrix

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Children:

Common: Quaternion/Mat2Q
Math: Linear/Cross
Math: Linear/Unit