LandingCost3D:

% Cost for the landing for a 3D planet problem.
 The cost is the weighted sum of total time and fuel mass.
 This is computed from the decision variable.
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   Form:
   cost = LandingCost3D( x, d )
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   Inputs
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   x       (:,1)   [beta;alpha;thrust;dT]
   d        (.)    Data structure describing spacecraft model

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   Outputs
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   cost    (1,1)   Time weighted with total fuel consumed

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