Totally parallel multilevel algorithms

Four totally parallel algorithms for the solution of a sparse linear system have common characteristics which become quite apparent when they are implemented on a highly parallel hypercube such as the CM2. These four algorithms are Parallel Superconvergent Multigrid (PSMG) of Frederickson and McBryan, Robust Multigrid (RMG) of Hackbusch, the FFT based Spectral Algorithm, and Parallel Cyclic Reduction. In fact, all four can be formulated as particular cases of the same totally parallel multilevel algorithm, which are referred to as TPMA. In certain cases the spectral radius of TPMA is zero, and it is recognized to be a direct algorithm. In many other cases the spectral radius, although not zero, is small enough that a single iteration per timestep keeps the local error within the required tolerance

From the Margins to the Mainstream: Human Rights and the Good Friday Agreement

This Essay examines the process by which the language of human rights moved to center stage in the political process. It looks to peace processes elsewhere to determine whether the Agreement is deserving of the High Commissioner\u27s special praise and analyzes, from a human rights perspective, the content of the Agreement and the extent to which the promises made therein have been fulfilled to date

Classical Heisenberg antiferromagnet on a garnet lattice: a Monte Carlo simulation

We have studied a classical antiferromagnet on a garnet lattice by means of Monte Carlo simulations in an attempt to examine the role of geometrical frustration in Gadolinium Gallium Garnet, Gd3Ga5O12 (GGG). Low-temperature specific heat, magnetisation, susceptibility, the autocorrelation function A(t) and the neutron scattering function S(Q) have been calculated for several models including different types of magnetic interactions and with the presence of an external magnetic field applied along the principal symmetry axes. A model, which includes only nearest-neighbour exchange, J1, neither orders down to the lowest temperature nor does it show any tendency towards forming a short-range coplanar spin structure. This model, however, does demonstrate a magnetic field induced ordering below T ~ 0.01 J1. In order to reproduce the experimentally observed properties of GGG, the simulated model must include nearest neighbour exchange interactions and also dipolar forces. The presence of weak next-to-nearest exchange interactions is found to be insignificant. In zero field S(Q) exhibits diffuse magnetic scattering around positions in reciprocal space where antiferromagnetic Bragg peaks appear in an applied magnetic field.Comment: 8 pages, 8 figures, to appear in PRB (JAN 2001

Pacific herring, Clupea harengus pallasi, studies in San Francisco and Tomales Bays, April 1987 to March 1988

Herring schools were surveyed hydroacoustically and sampled in San Francisco Bay from late October 1987 to March 1988. Nine large schools (greater than 1000 tons) and four smaller ones were detected. Total acoustic biomass estimate, using a combination of echo integration and "visual integration" methods, was 71,110 tons. Improved acoustic calibration parameters resulted in this estimate being close to the spawn escapement-plus-catch estimate of 68,881 tons. However, the two biomass survey methods ere complementary and, when used together, provide a more accurate estimate of the spawning population than either method alone. Eighty-two samples, containing a total of 16,316 herring, were collected with variable-mesh gill net, midwater trawl, or obtained from the roundhaul fishery. Mean body length decreased by more then 20 mm from the beginning to the end of the spawning season. Sex ratios favored males in November and December, while females were more abundant in February and March. The 1982 through 1986 year classes (6- through 2-yr olds) contributed approximately 98% by weight and number to the total 1987-88 spawning biomass in San Francisco Bay. Herring year classes aged 7 and older each comprised no more then 1% of any school. Above average recruitment occurred for the 1986 year class. Recruitment may not be complete for some year classes until age 3 yr. This was particularly evident for the 1985 year clear. (72pp.