Minimum Ultimate Band Design of Discrete Sliding Mode Control

The paper presents a generalized understanding on the dynamics of the sliding variable for discrete time sliding mode control systems via a fresh approach involving several bands in the space of the sliding variable. Using this analysis, controller parameters can be obtained once the ultimate band is chosen. It is shown that on choosing the least ultimate band, the control becomes non‐switching and Gao's reaching law becomes identical to Utkin's reaching law. On other occasions, the ultimate band obtained using this approach is clearly less than that obtained in previous works using Gao's reaching law. The analysis is presented for both state feedback and multirate output feedback cases.     

Bounded-Bypass Mutual Exclusion with Minimum Number of Registers

A mutual exclusion mechanism that is both fair and space efficient can be highly valuable for shared memory systems under time and memory constraints such as embedded real-time systems. Several algorithms that utilize only one shared variable and guarantee a certain level of fairness have been proposed. However, these use hypothetical read-modify-write operations that have never been implemented in any system. This paper presents two fair algorithms that do not use such operations, each of which uses a single additional shared variable. The proposed algorithms employ commonly available operations, fetch&store and read/write, on two shared variables. The first algorithm satisfies the bounded-bypass condition. The second is an improvement on the first that satisfies the FIFO condition, which is the most stringent fairness condition. Additionally, it is shown that achieving the bounded-bypass condition using the same set of operations requires two shared variables. Both of the algorithms are thus optimal with respect to the number of shared variables.     

Guest Editorial

The identification of continuous time models from non-uniformly sampled data records is investigated and a new identification algorithm based on the state variable filter approach is derived. It is shown that the orthogonal least squares estimator can be adapted for the identification of continuous time models from non-uniformly sampled data records and instrumental variables are introduced to reduce the bias in stochastic system identification. Multiplying the filtered variables obtained from the state variable filter, with higher powers of the noise free output signal prior to the estimation, is shown to enhance the parameter estimates. Simulated examples are included to illustrate the models.     

用C#.NET构建数字图像处理系统

采用C#．NET，能够方便地进行图像的读取、显示、存储；对图像进行处理时，可将图像的各个像素值读入数组中，处理完毕后的数组中的值写回图像中。以上的方法加上图像处理的具体算法以及C#．NET强大的图形界面能力，能够快速地构建一个图像处理系统。     

On-line multiversion database concurrency control

This paper presents a new model for studying the concurrency vs. computation time tradeoffs involved in on-line multiversion database concurrency control. The basic problem that is studied in our model is the following: Given:a current database system state which includes information such as which transaction previously read a version from which other transaction; which transaction has written which versions into the database; and the ordering of versions previously written; anda set of read and write requests of requesting transactions. Question: Does there exist a new database system state in which the requesting transactions can be immediately put into execution (their read and write requests satisfied, or in the case of predeclared writeset transactions, write requests are guaranteed to be satisfied) while preserving consistency under a given set of additional constraints? (The amount of concurrency achieved is defined by the set of additional constraints). In this paper we derive “limits” of performance achievable by polynomial time concurrency control algorithms. Each limit is characterized by a minimal set of constraints that allow the on-line scheduling problem to be solved in polynomial time. If any one constraint in that minimal set is omitted, although it could increase the amount of concurrency, it would also have the dramatic negative effect of making the scheduling problem NP-complete; whereas if we do not omit any constraint in the minimal set, then the scheduling problem can be solved in polynomial time. With each of these limits, one can construct an efficient scheduling algorithm that achieves an optimal level of concurrency in polynomial computation time according to the constraints defined in the minimal set.     

Migrating legacy scientific applications towards CORBA‐based client–server architectures

A distributed object is a reusable, self‐contained piece of software that cooperates with other objects on the same machine or across a network in a plug‐and‐play fashion via a well‐defined interface. The Numerical Propulsion System Simulation (NPSS) attempts to provide a collaborative aircraft engine design and simulation environment based on this concept. Many scientific applications in aerodynamics and solid mechanics are written in Fortran. Refitting this legacy Fortran code with distributed objects can increase code reusability. In this paper, we focus on the novel use of a remote variable scheme to help programmers migrate the Fortran code towards a client–server architecture. This scheme gives the client the capability of accessing variables at the server site and makes it easier for programmers to couple component engine code. Through the operator overloading features in C++, remote variables can be used in much the same way as traditional variables. The remote variable scheme adopts the lazy update approach and the prefetch method. Preliminary performance evaluation shows that communication overhead can be greatly reduced. Copyright © 2001 John Wiley & Sons, Ltd.     

On space-optimality of buffer-based conflict-free constructions of 1-writer 1-reader multivalued atomic variables from safe bits

A shared variable construction is called buffer-based if the values of the variable are stored in buffers that are different from control storage. Each buffer stores only a single value from the domain of the variable. A buffer-based construction is conflict-free if, in each execution of the shared variable, no reading of any buffer overlaps with any writing of that buffer. This paper studies shared space requirements for wait-free, conflict-free, deterministic constructions of 1-writer 1-reader multivalued atomic variables from safe variables. That four buffers are necessary and sufficient for such constructions has been established in the literature. This paper establishes the requirement for control storage. The least shared space for such a construction in the literature is (four safe buffers and) four safe control bits. We show that four safe control bits are necessary for such constructions when the reader is restricted to read at most one buffer in each read operation.     

Decompositions of four variable Boolean functions

All the decompositions of a Boolean function of four variables can be determined directly from its prime implicants if it is decomposable with one free variable. Decompositions of functions of three variables can be obtained from the column ratio of the variables.     

Reading many variables in one atomic operation: solutions withlinear or sublinear complexity

We address the problem of reading several variables (components) X ₁,...,X_c, all in one atomic operation, by only one process, called the reader, while each of these variables are being written by a set of writers. All operations (i.e., both reads and writes) are assumed to be totally asynchronous and wait-free. For this problem, only algorithms that require at best quadratic time and space complexity can be derived from the existing literature. (The time complexity of a construction is the number of suboperations of a high-level operation and its space complexity is the number of atomic shared variables it needs) In this paper, we provide a deterministic protocol that has linear (in the number of processes) space complexity, linear time complexity for a read operation, and constant time complexity for a write. Our solution does not make use of time-stamps. Rather, it is the memory location where a write writes that differentiates it from the other writes. Also, introducing randomness in the location where the reader gets the value that it returns, we get a conceptually very simple probabilistic algorithm. This algorithm has an overwhelmingly small, controllable probability of error. Its space complexity, and also the time complexity of a read operation, are sublinear. The time complexity of a write is constant. On the other hand, under the Archimedean time assumption, we get a protocol whose time and space complexity do not depend on the number of writers, but are linear in the number of components only. (The time complexity of a write operation is still constant.)     

The compleat requirements analyste [requirements analysis]

Recently a requirements analyst told me that be was far too busy to read anything except technical books and articles; after all, isn't that how we improve our skill? But requirements are concerned with much more than technical solutions, and building successful products depends on being able to broadly view the world and the people in it. You can improve your ability to communicate by reading as much as you can about diverse subjects. The author explains how this exogenous attitude enhances our systems requirements skills.     

Efficient algorithms for checking the atomicity of a run of read and write operations

LetX ₁,...,X _c be variables shared by a number of processorsP ₁,...,P _q that operate in a totally asynchronous and wait-free manner. An operation by a processor is either a write to one of the variables or a read of the values ofall variables. Operations arenot assumed to be instantaneous and may arbitrarily overlap in time. A succession of possibly overlapping operationsa ₁,...,a _n (i.e., a run) is said to be atomic, if these operations can be serialized in a way compatible with any existing precedences among them and so that any read operation returns for each variable the value of the most recent — with respect to the serialization — write operation on this variable. This paper examines the complexity of the combinatorial problem of testing a run for atomicity. First, it is pointed out that when there is only one shared variable or when only one processor is allowed to write to each variable, known theorems lead to polynomial-time algorithms for checking the atomicity of a run (the variable of the time-complexity function is the number of operations in the run). It is then proved that checking atomicity has polynomial-time complexity in the general case of more than one variables and with all processors allowed to read and write each variable. For the proof, the atomicity problem is reduced to the problem of consecutive 1s in matrices. The reduction entails showing a combinatorial result that might be interesting on its own.The research of the first author was partially supported by the European Union ESPRIT Basic Research Projects ALCOM II (contract no. 7141) and Insight II (contract no. 6019).The research of the second author was carried out while he was a student at the University of Patras and also during subsequent visits of his to Patras.     

Deep and shallow binding: The assignment operation

Programming languages which use dynamic identification for free variables (i.e., non-local references) are generally implemented with a deep or shallow binding variable access strategy. In this paper, variable access through the binding environment is assumed to be desirable. Given this assumption, it is demonstrated that the act of assigning values to variables may yield unexpected results for some of the binding strategies when functional arguments and results are used. A number of variations of deep and shallow binding strategies are examined along with the modifications necessary to implement the assignment operation in the expected manner.     

基于条件值的C/C++预处理测试算法

传统C/C++代码的预处理分析利用符号执行推断预处理中自由变量条件表达式的值,但是该算法的时间复杂度是指数型的.为降低时间复杂度,提出一种快速符号执行算法.源代码通过词法分析器得到顶处理变量和路径条件,为预处理变量建立节点,把路径条件转化为条件表达式,通过符号执行算法将两者整合为条件值c-value的形式,最终显示预处...     

The application of data mining techniques to model visual distraction of bicyclists

This paper presents a novel approach to modelling visual distraction of bicyclists. A unique bicycle simulator equipped with sensors capable of capturing the behaviour of the bicyclist is presented. While cycling two similar scenario routes, once while simultaneously interacting with an electronic device and once without any electronic device, statistics of the measured speed, head movements, steering angle and bicycle road position along with questionnaire data are captured. These variables are used to model the self-assessed distraction level of the bicyclist. Data mining techniques based on random forests, support vector machines and neural networks are evaluated for the modelling task. Out of the total 71 measured variables a variable selection procedure based on random forests is able to select a fraction of those and consequently improving the modelling performance. By combining the random forest-based variable selection and support vector machine-based modelling technique the best overall performance is achieved. The method shows that with a few observable variables it is possible to use machine learning to model, and thus predict, the distraction level of a bicyclist.     

MetaModel: a program for modelling and control analysis of metabolic pathways on the IBM PC and compatibles

MetaModel is a user-friendly program for calculating steady-state fluxes and metabolite concentrations of metabolic systems on the IBM PC and compatible computers. For any steady state that is obtained, one can then calculate a matrix of elasticity coefficients at that steady state, or a matrix of control and response coefficients. It thus offers a simple way to calculate the control structure of a pathway: it provides not only an educational tool that allows the student to verify empirically the classic summation relationships of metabolic control analysis but also a research tool for addressing 'what if?' questions about the behaviour of metabolic systems. Results can not only be printed or stored in a file, but can also be written to a special file that can be read by popular spreadsheet programs, thereby giving access to rapid, flexible and powerful methods for subsequent analysis and plotting of these results.     

Imposing shift-invariance using Flexible Structure Dictionary Learning (FSDL)

Sparse representation and Dictionary learning have attracted a lot of research attention in the last couple of decades and have provided state of the art results in many fields such as denoising, classification, inpainting and compression. However, applying general dictionary learning such as Method of Optimal Directions and Recursive Least Squares Dictionary Learning Algorithm can be computationally expensive, due to the large amount of free variables to be learned. Also sometimes the signal class has obvious repetitive structure which could benefit from a structured dictionary. One way to deal with these shortcomings is to impose a structure on the dictionary itself, for example the dictionary can be sparse or the atoms can be shift-invariant. In practice, imposing a structure means limiting the number of free variables. There are many examples of structured dictionaries such as double sparsity model or shift-invariant dictionaries. We have recently proposed a closed form solution to impose arbitrary structures onto a dictionary, called Flexible Structure Dictionary Learning. In this paper, we use this method to impose shift-invariant structure when training a dictionary. This structure allows us to not only simplify the original solution and make it computationally feasible to be used for large signals but also extend the concept of shift-invariance to include variable sized shifts in different atoms. The proposed dictionary update step finds all the free variables in all the atoms jointly, whereas some shift-invariant structured dictionaries in the recent literature, update one atom at a time. We have compared our proposed method with a general dictionary learning method and another shift-invariant method. Results show that signal approximation can be a promising application.     

Kernel-based hard clustering methods in the feature space with automatic variable weighting

This paper presents variable-wise kernel hard clustering algorithms in the feature space in which dissimilarity measures are obtained as sums of squared distances between patterns and centroids computed individually for each variable by means of kernels. The methods proposed in this paper are supported by the fact that a kernel function can be written as a sum of kernel functions evaluated on each variable separately. The main advantage of this approach is that it allows the use of adaptive distances, which are suitable to learn the weights of the variables on each cluster, providing a better performance. Moreover, various partition and cluster interpretation tools are introduced. Experiments with synthetic and benchmark datasets show the usefulness of the proposed algorithms and the merit of the partition and cluster interpretation tools.     

Robustness of multivariable discrete-time variable structure control

A robust stability criterion for multivariable discrete-time variable structure control is proposed. When a variable structure controller is designed and implemented as a sampled-data system, achieving robustness to uncertainties can become difficult. To ameliorate the situation, an uncertainty estimator, also formulated within the variable structure framework, can be used as an embedded discrete-time variable structure controller. This approach requires a bounded changing rate of the uncertainties to ensure robust stability. However, when uncertainties vary as a function of state variables, which occurs with parametric uncertainties, it is not practical to assume such a bound. In this paper, uncertainties are assumed to consist of external disturbances and parametric uncertainties. An uncertainty compensator is used to deal with the former, and a robust stability criterion is developed using the small gain theorem for the latter.