1,213 research outputs found
Need a Lift? An Elevator Queueing Problem
Various aspects of the behavior and dispatching of elevators (lifts) were studied. Monte Carlo simulation was used to study the statistics of the several models for the peak demand at uppeak times. Analytical models problems were used to prove or disprove whether schemes were optimal. A mostly integer programming problem was formulated but not studied further
Action semantics of unified modeling language
The Uni ed Modeling Language or UML, as a visual and general purpose modeling
language, has been around for more than a decade, gaining increasingly wide application
and becoming the de-facto industrial standard for modeling software systems. However,
the dynamic semantics of UML behaviours are only described in natural languages.
Speci cation in natural languages inevitably involves vagueness, lacks reasonability and
discourages mechanical language implementation. Such semi-formality of UML causes
wide concern for researchers, including us.
The formal semantics of UML demands more readability and extensibility due to its
fast evolution and a wider range of users. Therefore we adopt Action Semantics (AS),
mainly created by Peter Mosses, to formalize the dynamic semantics of UML, because
AS can satisfy these needs advantageously compared to other frameworks.
Instead of de ning UML directly, we design an action language, called ALx, and
use it as the intermediary between a typical executable UML and its action semantics.
ALx is highly heterogeneous, combining the features of Object Oriented Programming
Languages, Object Query Languages, Model Description Languages and more complex
behaviours like state machines. Adopting AS to formalize such a heterogeneous language
is in turn of signi cance in exploring the adequacy and applicability of AS.
In order to give assurance of the validity of the action semantics of ALx, a prototype
ALx-to-Java translator is implemented, underpinned by our formal semantic description
of the action language and using the Model Driven Approach (MDA). We argue that
MDA is a feasible way of implementing this source-to-source language translator because
the cornerstone of MDA, UML, is adequate to specify the static aspect of programming
languages, and MDA provides executable transformation languages to model mapping
rules between languages.
We also construct a translator using a commonly-used conventional approach, in
i
which a tool is employed to generate the lexical scanner and the parser, and then
other components including the type checker, symbol table constructor, intermediate
representation producer and code generator, are coded manually. Then we compare the
conventional approach with the MDA. The result shows that MDA has advantages over
the conventional method in the aspect of code quality but is inferior to the latter in
terms of system performance
Synthesis of Minimal Error Control Software
Software implementations of controllers for physical systems are at the core
of many embedded systems. The design of controllers uses the theory of
dynamical systems to construct a mathematical control law that ensures that the
controlled system has certain properties, such as asymptotic convergence to an
equilibrium point, while optimizing some performance criteria. However, owing
to quantization errors arising from the use of fixed-point arithmetic, the
implementation of this control law can only guarantee practical stability:
under the actions of the implementation, the trajectories of the controlled
system converge to a bounded set around the equilibrium point, and the size of
the bounded set is proportional to the error in the implementation. The problem
of verifying whether a controller implementation achieves practical stability
for a given bounded set has been studied before. In this paper, we change the
emphasis from verification to automatic synthesis. Using synthesis, the need
for formal verification can be considerably reduced thereby reducing the design
time as well as design cost of embedded control software.
We give a methodology and a tool to synthesize embedded control software that
is Pareto optimal w.r.t. both performance criteria and practical stability
regions. Our technique is a combination of static analysis to estimate
quantization errors for specific controller implementations and stochastic
local search over the space of possible controllers using particle swarm
optimization. The effectiveness of our technique is illustrated using examples
of various standard control systems: in most examples, we achieve controllers
with close LQR-LQG performance but with implementation errors, hence regions of
practical stability, several times as small.Comment: 18 pages, 2 figure
Supporting the evolution of software
2+122hlm.;24c
A real-time, dual processor simulation of the rotor system research aircraft
A real-time, man-in-the loop, simulation of the rotor system research aircraft (RSRA) was conducted. The unique feature of this simulation was that two digital computers were used in parallel to solve the equations of the RSRA mathematical model. The design, development, and implementation of the simulation are documented. Program validation was discussed, and examples of data recordings are given. This simulation provided an important research tool for the RSRA project in terms of safe and cost-effective design analysis. In addition, valuable knowledge concerning parallel processing and a powerful simulation hardware and software system was gained
Progress in AI Planning Research and Applications
Planning has made significant progress since its inception in the 1970s, in terms both of the efficiency and sophistication of its algorithms and representations and its potential for application to real problems. In this paper we sketch the foundations of planning as a sub-field of Artificial Intelligence and the history of its development over the past three decades. Then some of the recent achievements within the field are discussed and provided some experimental data demonstrating the progress that has been made in the application of general planners to realistic and complex problems. The paper concludes by identifying some of the open issues that remain as important challenges for future research in planning
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