Dual number-based variational data assimilation: Constructing exact tangent linear and adjoint code from nonlinear model evaluations.

Dual number-based variational data assimilation: Constructing exact tangent linear and adjoint code from nonlinear model evaluations.

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Dual numbers allow for automatic, exact evaluation of the Armored Vehicle Kit numerical derivative of high-dimensional functions at an arbitrary point with minimal coding effort.We use dual numbers to construct tangent linear and adjoint model code for a biogeochemical ocean model and apply it to a variational (4D-Var) data assimilation system when coupled to a realistic physical ocean circulation model with existing data assimilation capabilities.The resulting data assimilation system takes modestly longer to run click here than its hand-coded equivalent but is considerably easier to implement and updates automatically when modifications are made to the biogeochemical model, thus making its maintenance with code changes trivial.