13,404 research outputs found
CAutoCSD-evolutionary search and optimisation enabled computer automated control system design
This paper attempts to set a unified scene for various linear time-invariant (LTI) control system design schemes, by transforming the existing concept of 'Computer-Aided Control System Design' (CACSD) to the novel 'Computer-Automated Control System Design' (CAutoCSD). The first step towards this goal is to accommodate, under practical constraints, various design objectives that are desirable in both time and frequency-domains. Such performance-prioritised unification is aimed to relieve practising engineers from having to select a particular control scheme and from sacrificing certain performance goals resulting from pre-committing to the adopted scheme. With the recent progress in evolutionary computing based extra-numeric, multi-criterion search and optimisation techniques, such unification of LTI control schemes becomes feasible, analytically and practically, and the resultant designs can be creative. The techniques developed are applied to, and illustrated by, three design problems. The unified approach automatically provides an integrator for zero-steady state error in velocity control of a DC motor, meets multiple objectives in designing an LTI controller for a non-minimum phase plant and offers a high-performing LTI controller network for a nonlinear chemical process
Automating control system design via a multiobjective evolutionary algorithm
This chapter presents a performance-prioritized computer aided control system design (CACSD) methodology using a multi-objective evolutionary algorithm. The evolutionary CACSD approach unifies different control laws in both the time and frequency domains based upon performance satisfactions, without the need of aggregating different design criteria into a compromise function. It is shown that control engineers' expertise as well as settings on goal or priority for different preference on each performance requirement can be easily included and modified on-line according to the evolving trade-offs, which makes the controller design interactive, transparent and simple for real-time implementation. Advantages of the evolutionary CACSD methodology are illustrated upon a non-minimal phase plant control system, which offer a set of low-order Pareto optimal controllers satisfying all the conflicting performance requirements in the face of system constraints
A correct, precise and efficient integration of set-sharing, freeness and linearity for the analysis of finite and rational tree languages
It is well known that freeness and linearity information positively interact with aliasing information, allowing both the precision and the efficiency of the sharing analysis of logic programs to be improved. In this paper, we present a novel combination of set-sharing with freeness and linearity information, which is characterized by an improved abstract unification operator. We provide a new abstraction function and prove the correctness of the analysis for both the finite tree and the rational tree cases.
Moreover, we show that the same notion of redundant information as identified in Bagnara et al. (2000) and Zaffanella et al. (2002) also applies to this abstract domain combination: this allows for the implementation of an abstract unification operator running in polynomial time and achieving the same precision on all the considered observable properties
Unification and Matching on Compressed Terms
Term unification plays an important role in many areas of computer science,
especially in those related to logic. The universal mechanism of grammar-based
compression for terms, in particular the so-called Singleton Tree Grammars
(STG), have recently drawn considerable attention. Using STGs, terms of
exponential size and height can be represented in linear space. Furthermore,
the term representation by directed acyclic graphs (dags) can be efficiently
simulated. The present paper is the result of an investigation on term
unification and matching when the terms given as input are represented using
different compression mechanisms for terms such as dags and Singleton Tree
Grammars. We describe a polynomial time algorithm for context matching with
dags, when the number of different context variables is fixed for the problem.
For the same problem, NP-completeness is obtained when the terms are
represented using the more general formalism of Singleton Tree Grammars. For
first-order unification and matching polynomial time algorithms are presented,
each of them improving previous results for those problems.Comment: This paper is posted at the Computing Research Repository (CoRR) as
part of the process of submission to the journal ACM Transactions on
Computational Logic (TOCL)
Methods for Rapidly Processing Angular Masks of Next-Generation Galaxy Surveys
As galaxy surveys become larger and more complex, keeping track of the
completeness, magnitude limit, and other survey parameters as a function of
direction on the sky becomes an increasingly challenging computational task.
For example, typical angular masks of the Sloan Digital Sky Survey contain
about N=300,000 distinct spherical polygons. Managing masks with such large
numbers of polygons becomes intractably slow, particularly for tasks that run
in time O(N^2) with a naive algorithm, such as finding which polygons overlap
each other. Here we present a "divide-and-conquer" solution to this challenge:
we first split the angular mask into predefined regions called "pixels," such
that each polygon is in only one pixel, and then perform further computations,
such as checking for overlap, on the polygons within each pixel separately.
This reduces O(N^2) tasks to O(N), and also reduces the important task of
determining in which polygon(s) a point on the sky lies from O(N) to O(1),
resulting in significant computational speedup. Additionally, we present a
method to efficiently convert any angular mask to and from the popular HEALPix
format. This method can be generically applied to convert to and from any
desired spherical pixelization. We have implemented these techniques in a new
version of the mangle software package, which is freely available at
http://space.mit.edu/home/tegmark/mangle/, along with complete documentation
and example applications. These new methods should prove quite useful to the
astronomical community, and since mangle is a generic tool for managing angular
masks on a sphere, it has the potential to benefit terrestrial mapmaking
applications as well.Comment: New version 2.1 of the mangle software now available at
http://space.mit.edu/home/tegmark/mangle/ - includes galaxy survey masks and
galaxy lists for the latest SDSS data release and the 2dFGRS final data
release as well as extensive documentation and examples. 14 pages, 9 figures,
matches version accepted by MNRA
Four Lessons in Versatility or How Query Languages Adapt to the Web
Exposing not only human-centered information, but machine-processable data on the Web is one of the commonalities of recent Web trends. It has enabled a new kind of applications and businesses where the data is used in ways not foreseen by the data providers. Yet this exposition has fractured the Web into islands of data, each in different Web formats: Some providers choose XML, others RDF, again others JSON or OWL, for their data, even in similar domains. This fracturing stifles innovation as application builders have to cope not only with one Web stack (e.g., XML technology) but with several ones, each of considerable complexity. With Xcerpt we have developed a rule- and pattern based query language that aims to give shield application builders from much of this complexity: In a single query language XML and RDF data can be accessed, processed, combined, and re-published. Though the need for combined access to XML and RDF data has been recognized in previous work (including the W3C’s GRDDL), our approach differs in four main aspects: (1) We provide a single language (rather than two separate or embedded languages), thus minimizing the conceptual overhead of dealing with disparate data formats. (2) Both the declarative (logic-based) and the operational semantics are unified in that they apply for querying XML and RDF in the same way. (3) We show that the resulting query language can be implemented reusing traditional database technology, if desirable. Nevertheless, we also give a unified evaluation approach based on interval labelings of graphs that is at least as fast as existing approaches for tree-shaped XML data, yet provides linear time and space querying also for many RDF graphs. We believe that Web query languages are the right tool for declarative data access in Web applications and that Xcerpt is a significant step towards a more convenient, yet highly efficient data access in a “Web of Data”
Control Barrier Function Based Quadratic Programs for Safety Critical Systems
Safety critical systems involve the tight coupling between potentially
conflicting control objectives and safety constraints. As a means of creating a
formal framework for controlling systems of this form, and with a view toward
automotive applications, this paper develops a methodology that allows safety
conditions -- expressed as control barrier functions -- to be unified with
performance objectives -- expressed as control Lyapunov functions -- in the
context of real-time optimization-based controllers. Safety conditions are
specified in terms of forward invariance of a set, and are verified via two
novel generalizations of barrier functions; in each case, the existence of a
barrier function satisfying Lyapunov-like conditions implies forward invariance
of the set, and the relationship between these two classes of barrier functions
is characterized. In addition, each of these formulations yields a notion of
control barrier function (CBF), providing inequality constraints in the control
input that, when satisfied, again imply forward invariance of the set. Through
these constructions, CBFs can naturally be unified with control Lyapunov
functions (CLFs) in the context of a quadratic program (QP); this allows for
the achievement of control objectives (represented by CLFs) subject to
conditions on the admissible states of the system (represented by CBFs). The
mediation of safety and performance through a QP is demonstrated on adaptive
cruise control and lane keeping, two automotive control problems that present
both safety and performance considerations coupled with actuator bounds
Sensitivity of IceCube-DeepCore to neutralino dark matter in the MSSM-25
We analyse the sensitivity of IceCube-DeepCore to annihilation of neutralino
dark matter in the solar core, generated within a 25 parameter version of the
minimally supersymmetric standard model (MSSM-25). We explore the
25-dimensional parameter space using scanning methods based on importance
sampling and using DarkSUSY 5.0.6 to calculate observables. Our scans produced
a database of 6.02 million parameter space points with neutralino dark matter
consistent with the relic density implied by WMAP 7-year data, as well as with
accelerator searches. We performed a model exclusion analysis upon these points
using the expected capabilities of the IceCube-DeepCore Neutrino Telescope. We
show that IceCube-DeepCore will be sensitive to a number of models that are not
accessible to direct detection experiments such as SIMPLE, COUPP and XENON100,
indirect detection using Fermi-LAT observations of dwarf spheroidal galaxies,
nor to current LHC searches.Comment: 15 pages, 13 figures. V2: Additional comparisons are made to limits
from Fermi-LAT observations of dwarf spheroidal galaxies and to the 125 GeV
Higgs signal from the LHC. The spectral hardness section has been removed.
Matches version accepted for publication in JCAP. V3: Typos correcte
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