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   Computes residual dipole torques.
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   Form:
   t = TRD( m, b )
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   Inputs
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   m                  (3,n or 1) Dipoles (ATM^2)
   b                  (3,n or 1) Magnetic field (T)

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   Outputs
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   t                  (3,1)      Torque (Nm)

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