WOLFRAM SYSTEMMODELER
    AtanLibLibrary for the atan3 function which is double differentiable  | 
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         Four quadrant inverse tangent (select solution that is closest to given angle y0)  | 
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         second deviation of atan3  | 
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         First deviation of atan3  | 
    

SystemModel["PlanarMechanics.Utilities.AtanLib"]
