Bringing Together Automatic Differentiation and OpenMP.

Abstract

Derivatives of almost arbitrary functions can be evaluated efficiently by automatic differentiation whenever the functions are given in the form of computer programs in a high-level programming language such as Fortran, C, or C++. Furthermore, in contrast to numerical differentiation where derivatives are approximated, automatic differentiation generates derivatives that are accurate up to machine precision. The so-called forward mode of automatic differentiation computes derivatives by carrying forward a gradient associated with each intermediate variable simultaneously with the evaluation of the function itself. It is shown how software tools implementing the technology of automatic differentiation can benefit from simple concepts of shared memory programming to parallelize the gradient operations. The feasibility of our approach is demonstrated by numerical experiments. They were performed with a code that was generated automatically by the Adifor system and augmented with OpenMP directives.