RadialOscillation:

% Compute the radial oscillation of the relative motion using Hills eqns.

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   Inputs
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   z0      (1,1)   Initial relative cross-track position
   x0Dot   (1,1)   Initial relative velocity (radial direction)
   z0Dot   (1,1)   Initial relative velocity (cross-track direction)
   n       (1,1)   Mean orbit rate

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   Outputs
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   r       (1,1)   Radial amplitude of oscillation

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