Applications of Conformal Computing techniques to problems in computational physics: the Fast Fourier Transform

The techniques of Conformal Computing are introduced with an application to the Fast Fourier Transform. Conformal Computing is a design methodology, based on a rigorous mathematical foundation, which provides a systematic approach to the most efficient organization of all levels of the software and hardware design hierarchy from high-level software constructs all the way down to the design of the integrated circuits. We show that using these general design principles, without any specialized optimization, leads to portable, scalable, code that is competitive with other well-tuned machine specific routines. Further improvements are straightforward within our formalism by taking into account specific hardware details (e.g., cache loops) in a portable parametric way. We also argue that the present theory constitutes a uniform way of reasoning about physics and the data structures that define physics on computers.     

What determines static friction and controls the transition to sliding?

We studied the shear response of a confined lubricant layer on approach of the transition to sliding with a surface force apparatus modified for oscillatory shear. In a given experiment, we found that the transition to sliding occurred always around the same deformation amplitude although the shear stress needed to initiate sliding varied up to a factor of two depending on sample history. This suggests the concept of deformation-controlled switching from rest to sliding. The elastic spring-constant, in the stick state, weakened with increasing deformation amplitude. This decrease can be described by a power law when plotted versus the distance to a critical deformation amplitude. The build-up of solid-like behavior after sliding stopped was also gradual and was consistent with a logarithmic time dependence. We suggest a model relating the gradual decrease of stiffness to weakening of the boundary layer, specifically to destruction of some elastic links between molecules or between molecules and the solid surfaces. Static friction (the force that must be overcome at the onset of kinetic motion) is proportional to the number of such links formed during the time of stick.     

Abstracts

Journal of the American Oil Chemists' Society -     

Translation and Run-Time Validation of Loop Transformations

This paper presents new approaches to the validation of loop optimizations that compilers use to obtain the highest performance from modern architectures. Rather than verify the compiler, the approach of translation validationperforms a validation check after every run of the compiler, producing a formal proof that the produced target code is a correct implementation of the source code. As part of an active and ongoing research project on translation validation, we have previously described approaches for validating optimizations that preserve the loop structure of the code and have presented a simulation-based general technique for validating such optimizations. In this paper, for more aggressive optimizations that alter the loop structure of the code—such as distribution, fusion, tiling, and interchange—we present a set of permutation ruleswhich establish that the transformed code satisfies all the implied data dependencies necessary for the validity of the considered transformation. We describe the extensions to our tool voc-64 which are required to validate these structure-modifying optimizations. This paper also discusses preliminary work on run-time validation of speculative loop optimizations. This involves using run-time tests to ensure the correctness of loop optimizations whose correctness cannot be guaranteed at compile time. Unlike compiler validation, run-time validation must not only determine when an optimization has generated incorrect code, but also recover from the optimization without aborting the program or producing an incorrect result. This technique has been applied to several loop optimizations, including loop interchange and loop tiling, and appears to be quite promising. This research was supported in part by NSF grant CCR-0098299, ONR grant N00014-99-1-0131, and the John von Neumann Minerva Center for Verification of Reactive Systems.     

Reliability of Holland codes across interest measures for adult females.

Derived 8 3-letter codes representing J. L. Holland's (1973) personality types from 3 inventories: the Self-Directed Search, the Strong-Campbell Interest Inventory (3 types of scales), and the Kuder Occupational Interest Survey (4 types of scales) for each of 52 adult women. Comparisons between codes derived from these sources revealed that agreement between any 2 sources of codes was varied. Some pairs agreed to the extent that the 3 letters of the codes were the same although not in the same order; others agreed to the extent that the 1st 2 letters matched 2 from the other. Findings support Holland's injunction to consider all codes that may be derived from the 3 highest ranking types rather than to limit consideration to occupations related to the code in only the order produced by the instrument. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)