tr-announce Juli 2007

tr-announce@lists.rwth-aachen.de

1 Teilnehmer
4 Diskussionen

2007-11: 6. Fachgespräch Sensornetzwerke

von Peter Schneider-Kamp

The following technical report is available from http://aib.informatik.rwth-aachen.de: 6. Fachgespräch Sensornetzwerke Klaus Wehrle (editor) AIB 2007-11 This report contains the proceedings of the 6. Fachgespräch Sensornetzwerke of the der GI/ITG Fachgruppe "Kommunikation und Verteilte Systeme", which was held on July 16-17, 2007 in Aachen, Germany.

16 Jahre, 9 Monate

2007-14: OpenAD/F: A Modular, Open-Source Tool for Automatic Differentiation of Fortran Codes

von Peter Schneider-Kamp

The following technical report is available from http://aib.informatik.rwth-aachen.de: OpenAD/F: A Modular, Open-Source Tool for Automatic Differentiation of Fortran Codes Jean Utke, Uwe Naumann, Mike Fagan, Nathan Tallent, Michelle Strout, Patrick Heimbach, Chris Hill, and Carl Wunsch AIB 2007-14 The OpenAD/F tool allows the evaluation of derivatives of functions defined by a Fortran program. The derivative evaluation is performed by a Fortran code resulting from the analysis and transformation of the original program that defines the function of interest. OpenAD/F has been designed with a particular emphasis on modularity, flexibility, and the use of open source components. While the code transformation follows the basic principles of automatic differentiation, the tool implements new algorithmic approaches at various levels, for example, for basic block preaccumulation and call graph reversal. Unlike most other automatic differentiation tools, OpenAD/F uses components provided by the OpenAD framework, which supports a comparatively easy extension of the code transformations in a language-independent fashion. It uses code analysis results implemented in the OpenAnalysis component. The interface to the language-independent transformation engine is an XML-based format, specified through an XML schema. The implemented transformation algorithms allow efficient derivative computations using locally optimized cross-country sequences of vertex, edge, and face elimination steps. Specifically, for the generation of adjoint codes, OpenAD/F supports various code reversal schemes with hierarchical checkpointing at the subroutine level. As an example from geophysical fluid dynamics a nonlinear time-dependent scalable, yet simple, barotropic ocean model is considered. OpenAD/F's reverse mode is applied to compute sensitivities of some of the model's transport properties with respect to gridded fields such as bottom topography as independent (control) variables.

16 Jahre, 9 Monate

2007-13: Second-Order Adjoints by Source Code Manipulation of Numerical Programs

von Peter Schneider-Kamp

The following technical report is available from http://aib.informatik.rwth-aachen.de: Second-Order Adjoints by Source Code Manipulation of Numerical Programs Uwe Naumann, Michael Maier, Jan Riehme, and Bruce Christianson AIB 2007-13 The analysis and modification of numerical programs in the context of generating and optimizing adjoint code automatically probably ranges among the technically and theoretically most challenging source transformation algorithms known today. A complete compiler for the target language (Fortran in our case) is needed to cover the technical side. This amounts to a mathematically motivated semantic transformation of the source code that involves the reversal of the flow of data through the program. Both the arithmetic complexity and the memory requirement can be substantial for large-scale numerical simulations. Finding the optimal data-flow reveral schedule turns out to be an NP-complete problem. The same complexity result applies to other domain-specific peephole optimizations. In this paper we present a first research prototype of the NAGWare Fortran compiler with the ability to generate adjoint code automatically. Moreover, we discuss an approach to generating second-order adjoint code for use in Newtontype algorithms for unconstrained nonlinear optimization. While the focus of this paper is mostly on the compiler issues some information on the mathematical background will be found helpful for motivational purposes.

16 Jahre, 9 Monate

2007-12: An L-Attributed Grammar for Adjoint Code

von Peter Schneider-Kamp

The following technical report is available from http://aib.informatik.rwth-aachen.de: An L-Attributed Grammar for Adjoint Code Uwe Naumann AIB 2007-12 Gradients of high-dimensional functions can be computed efficiently and with machine accuracy by so-called adjoint codes.We present an L-attributed grammar for the single-pass generation of intraprocedural adjoint code for a simple imperative language (a subset of C). Our ideas can easily be applied to any programming language that is suitable for syntax-directed translation. Moreover the conceptual insights are useful in the context of multi-pass generation of adjoint code. Our focus is on correctness. The necessary domain-specific code optimizations are beyond the scope of this paper. We give references to corresponding work in this area.

16 Jahre, 9 Monate

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tr-announce Juli 2007