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

Conference · Fri Dec 31 04:00:00 EST 1993

OSTI ID:93547

Bischof, C H

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.

• Research Organization: Argonne National Lab., IL (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: W-31109-ENG-38
• OSTI ID: 93547
• Report Number(s): ANL/MCS/CP--85787; CONF-9306285--2; ON: DE95013715
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
99 GENERAL AND MISCELLANEOUS
A CODES
AUTOMATION
CLIMATE MODELS
DIFFERENTIAL CALCULUS
FORTRAN
JACOBIAN FUNCTION
SERIES EXPANSION
WEATHER