Automatic differentiation, tangent linear models, and (pseudo) adjoints

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This paper provides a brief introduction to automatic differentiation and relates it to the tangent linear model and adjoint approaches commonly used in meteorology. After a brief review of the forward and reverse mode of automatic differentiation, the ADIFOR automatic differentiation tool is introduced, and initial results of a sensitivity-enhanced version of the MM5 PSU/NCAR mesoscale weather model are presented. We also present a novel approach to the computation of gradients that uses a reverse mode approach at the time loop level and a forward mode approach at every time step. The resulting ``pseudoadjoint`` shares the characteristic of an adjoint ... continued below

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22 p.

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Bischof, C.H. December 31, 1993.

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Description

This paper provides a brief introduction to automatic differentiation and relates it to the tangent linear model and adjoint approaches commonly used in meteorology. After a brief review of the forward and reverse mode of automatic differentiation, the ADIFOR automatic differentiation tool is introduced, and initial results of a sensitivity-enhanced version of the MM5 PSU/NCAR mesoscale weather model are presented. We also present a novel approach to the computation of gradients that uses a reverse mode approach at the time loop level and a forward mode approach at every time step. The resulting ``pseudoadjoint`` shares the characteristic of an adjoint code that the ratio of gradient to function evaluation does not depend on the number of independent variables. In contrast to a true adjoint approach, however, the nonlinearity of the model plays no role in the complexity of the derivative code.

Physical Description

22 p.

Notes

OSTI as DE95013715

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  • North Atlantic Treaty Organization/Advanced Study Institute (NATO/ASI) workshop in high performance computing in geosciences, Chamouix (France), 21-25 Jun 1993

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  • Other: DE95013715
  • Report No.: ANL/MCS/CP--85787
  • Report No.: CONF-9306285--2
  • Grant Number: W-31-109-ENG-38
  • Office of Scientific & Technical Information Report Number: 93547
  • Archival Resource Key: ark:/67531/metadc792904

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  • December 31, 1993

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  • Dec. 19, 2015, 7:14 p.m.

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  • Jan. 6, 2016, 2:44 p.m.

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Bischof, C.H. Automatic differentiation, tangent linear models, and (pseudo) adjoints, article, December 31, 1993; Illinois. (digital.library.unt.edu/ark:/67531/metadc792904/: accessed September 25, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.