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   Compute the magnetic field of a dipole
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   Form:
   b = Dipole( m, xD, x )
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   ------
   Inputs
   ------
   m             (3,1)   Magnetic dipole vector (ATM^2)
   xD            (3,1)   Location of the dipole (m)
   x             (3,:)   Points of interest (m)

   -------
   Outputs
   -------
   b             (3,:)   Magnetic field (T)

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