Universality of 2d Yukawa and Gross-Neveu models

Evidence for the same universal behavior of 2d Yukawa and Gross-Neveu models in a certain range of couplings, particularly for $\kappa<0$, is presented.Comment: 3 pages compressed uuencoded PostScript, to appear in the Proceedings of LATTICE '93 (Dallas), HLRZ 91/9

Optimizing sparse matrix-vector multiplication in NEC SX-Aurora vector engine

Sparse Matrix-Vector multiplication (SpMV) is an essential piece of code used in many High Performance Computing (HPC) applications. As previous literature shows, achieving efficient vectorization and performance in modern multi-core systems is nothing straightforward. It is important then to revisit the current stateof-the-art matrix formats and optimizations to be able to deliver deliver high performance in long vector architectures. In this tech-report, we describe how to develop an efficient implementation that achieves high throughput in the NEC Vector Engine: a 256 element-long vector architecture. Combining several pre-processing and kernel optimizations we obtain an average 12% improvement over a base SELLC-s implementation on a heterogeneous set of 24 matrices.Preprin

Reducing Kernel Development Complexity In Distributed Environments

Setting up generic and fully transparent distributed services for clusters implies complex and tedious kernel developments. More flexible approaches such as user-space libraries are usually preferred with the drawback of requiring application recompilation. A second approach consists in using specific kernel modules (such as FUSE in Gnu/Linux system) to transfer kernel complexity into user space. In this paper, we present a new way to design and implement kernel distributed services for clusters by using a cluster wide consistent data management service. This system, entitled kDDM for "kernel Distributed Data Management", offers flexible kernel mechanisms to transparently manage remote accesses, cache and coherency. We show how kDDM simplifies distributed kernel developments by presenting the design and the implementation of a service as complex as a fully symmetric distributed file system. The innovative approach of kDDM has the potential to boost the development of distributed kernel services because it relieves the developers of the burden of dealing with distributed protocols and explicit data transfers. Instead, it allows focusing on the implementation of services in a manner very similar to that of parallel programming on SMP systems. More generally, the use of kDDM could be exploited in almost all local kernel services to extend them to cluster scale. Cluster wide IPC, distributed namespaces (such as /proc) or process migration are some potential examples

Fermion-Higgs model with strong Wilson-Yukawa coupling in two dimensions

The fermion mass spectrum is studied in the quenched approximation in the strong coupling vortex phase (VXS) of a globally U(1)$_L \otimes$U(1)$_R$ symmetric scalar-fermion model in two dimensions. In this phase fermion doublers can be completely removed from the physical spectrum by means of a strong Wilson-Yukawa coupling. The lowest lying fermion spectrum in this phase consists most probably only of a massive Dirac fermion which has charge zero with respect to the $U(1)_L$ group. We give evidence that the fermion which is charged with respect to that subgroup is absent in the VXS phase. When the $U(1)_L$ gauge fields are turned on, the neutral fermion may couple chirally to the massive vector boson state in the confinement phase. The outcome is very similar to our findings in the strong coupling symmetric phase (PMS) of fermion-Higgs models with Wilson-Yukawa coupling in four dimensions, with the exception that in four dimensions the neutral fermion does most probably decouple from the bosonic bound states.Comment: 21 pages, 6 postscript figures (appended), Amsterdam ITFA 92-21, HLRZ J\"ulich 92-5