184 research outputs found
The lid method for exhaustive exploration of metastable states of complex systems
The `lid' algorithm performs an exhaustive exploration of neighborhoods of
local energy minima of energy landscapes. This paper describes an
implementation of the algorithm, including issues of parallel performance and
scalability. To illustrate the versatility of the approach and to stress the
common features present in landscapes of quite different systems, we present
selected results for 1) a spin glass, 2) a ferromagnet, 3) a covalent network
model for glassy systems, and 4) a polymer. The exponential nature of the local
density of states found in these systems and its relation to the ordering
transition is briefly commented upon.Comment: RevTeX, 11 pages, 1 figur
PSPI: streamlining 3D echo-reconstructive imaging
EchoÂreconstruction techniques for subsurface imaging, widely
used in oil exploration, are based on experiments in which short acoustic impulses, emitted at the surface, illuminate a certain volume and are backscattered by inhomogeneities of the medium. The inhomogeneities act as reflecting surfaces which cause signal echoing; the echoes are then recorded at the surface and processed through a propagation model (which acts as a “computational lens”) to yield an image of those very inhomogeneities.
Migration, based on the scalar wave equation, is the standard imaging technique for seismic applications [1]. In the migration process, the recorded pressure waves(called the seismic traces or the seismic section) are used as initial conditions for a wave field governed by the scalar wave equation in an inhomogeneous medium
MatlabMPI
The true costs of high performance computing are currently dominated by
software. Addressing these costs requires shifting to high productivity
languages such as Matlab. MatlabMPI is a Matlab implementation of the Message
Passing Interface (MPI) standard and allows any Matlab program to exploit
multiple processors. MatlabMPI currently implements the basic six functions
that are the core of the MPI point-to-point communications standard. The key
technical innovation of MatlabMPI is that it implements the widely used MPI
``look and feel'' on top of standard Matlab file I/O, resulting in an extremely
compact (~250 lines of code) and ``pure'' implementation which runs anywhere
Matlab runs, and on any heterogeneous combination of computers. The performance
has been tested on both shared and distributed memory parallel computers (e.g.
Sun, SGI, HP, IBM, Linux and MacOSX). MatlabMPI can match the bandwidth of C
based MPI at large message sizes. A test image filtering application using
MatlabMPI achieved a speedup of ~300 using 304 CPUs and ~15% of the theoretical
peak (450 Gigaflops) on an IBM SP2 at the Maui High Performance Computing
Center. In addition, this entire parallel benchmark application was implemented
in 70 software-lines-of-code, illustrating the high productivity of this
approach. MatlabMPI is available for download on the web
(www.ll.mit.edu/MatlabMPI).Comment: Download software from http://www.ll.mit.edu/MatlabMPI, 12 pages
including 7 color figures; submitted to the Journal of Parallel and
Distributed Computin
Spinodal decomposition of off-critical quenches with a viscous phase using dissipative particle dynamics in two and three spatial dimensions
We investigate the domain growth and phase separation of
hydrodynamically-correct binary immiscible fluids of differing viscosity as a
function of minority phase concentration in both two and three spatial
dimensions using dissipative particle dynamics. We also examine the behavior of
equal-viscosity fluids and compare our results to similar lattice-gas
simulations in two dimensions.Comment: 34 pages (11 figures); accepted for publication in Phys. Rev.
Agent-based resource management for grid computing
A computational grid is a hardware and software infrastructure that provides
dependable, consistent, pervasive, and inexpensive access to high-end
computational capability. An ideal grid environment should provide access to the
available resources in a seamless manner. Resource management is an important
infrastructural component of a grid computing environment. The overall aim of
resource management is to efficiently schedule applications that need to utilise the
available resources in the grid environment. Such goals within the high
performance community will rely on accurate performance prediction capabilities.
An existing toolkit, known as PACE (Performance Analysis and Characterisation
Environment), is used to provide quantitative data concerning the performance of
sophisticated applications running on high performance resources. In this thesis an
ASCI (Accelerated Strategic Computing Initiative) kernel application, Sweep3D,
is used to illustrate the PACE performance prediction capabilities. The validation
results show that a reasonable accuracy can be obtained, cross-platform
comparisons can be easily undertaken, and the process benefits from a rapid
evaluation time. While extremely well-suited for managing a locally distributed
multi-computer, the PACE functions do not map well onto a wide-area
environment, where heterogeneity, multiple administrative domains, and communication irregularities dramatically complicate the job of resource
management. Scalability and adaptability are two key challenges that must be
addressed.
In this thesis, an A4 (Agile Architecture and Autonomous Agents) methodology is
introduced for the development of large-scale distributed software systems with
highly dynamic behaviours. An agent is considered to be both a service provider
and a service requestor. Agents are organised into a hierarchy with service
advertisement and discovery capabilities. There are four main performance
metrics for an A4 system: service discovery speed, agent system efficiency,
workload balancing, and discovery success rate.
Coupling the A4 methodology with PACE functions, results in an Agent-based
Resource Management System (ARMS), which is implemented for grid
computing. The PACE functions supply accurate performance information (e. g.
execution time) as input to a local resource scheduler on the fly. At a meta-level,
agents advertise their service information and cooperate with each other to
discover available resources for grid-enabled applications. A Performance
Monitor and Advisor (PMA) is also developed in ARMS to optimise the
performance of the agent behaviours.
The PMA is capable of performance modelling and simulation about the agents in
ARMS and can be used to improve overall system performance. The PMA can
monitor agent behaviours in ARMS and reconfigure them with optimised
strategies, which include the use of ACTs (Agent Capability Tables), limited
service lifetime, limited scope for service advertisement and discovery, agent
mobility and service distribution, etc.
The main contribution of this work is that it provides a methodology and
prototype implementation of a grid Resource Management System (RMS). The
system includes a number of original features that cannot be found in existing
research solutions
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