DUnit:

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   Derivative of the unit vector for r.
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   Form:
   u = DUnit( r, v )
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   ------
   Inputs
   ------
   r             (3,:)   Vectors
   v             (3,:)   Vector derivatives

   -------
   Outputs
   -------
   u             (3,:)   Unit vector derivatives

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Children:

Common: Math/Dot
Common: Math/Mag
Common: Math/SXV