Building the Tangent and Adjoint codes of the Ocean General Circulation Model OPA with the Automatic Differentiation tool TAPENADE

Moulay Hicham Tber Laurent Hascoët Benjamin Dauvergne (INRIA, BP93, 06902 Sophia-Antipolis, France) Arthur Vidard (INRIA-LJK, Grenoble, France)

INRIA Research Report #6372, november 2007 (28 pages)

Abstract: The ocean general circulation model OPA is developed by the LODYC team at Paris VI university. OPA has recently undergone a major rewriting, migrating to FORTRAN95, and its adjoint code needs to be rebuilt. For earlier versions, the adjoint of OPA was written by hand at a high development cost. We use the Automatic Differentiation tool TAPENADE to build mechanicaly the tangent and adjoint codes of OPA. We validate the differentiated codes by comparison with divided differences, and also with an identical twin experiment. We apply state-of-the-art methods to improve the performance of the adjoint code. In particular we implement the Griewank and Walther's binomial checkpointing algorithm which gives us an optimal trade-off between time and memory consumption. We apply a specific strategy to differentiate the iterative linear solver that comes from the implicit time stepping scheme.

Keywords: OPA, general circulation model, TAPENADE, Automatic Differentiation, reverse mode, Adjoint Code, Checkpointing

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@techreport{TberEtAl07,
  author = {Tber, M.-H. and Hasco{\"e}t, L. and Vidard, A. and Dauvergne, B.},
  title = {Building the Tangent and Adjoint codes of the Ocean General Circulation Model {OPA} with the Automatic Differentiation tool TAPENADE},
  institution = {INRIA},
  type = {Research Report},
  number= 6372,
  url = "https://hal.inria.fr/inria-00192415",
  year=2007
}