This paper presents a brief overview of the field of evolutionary computation. Three major research areas of evolutionary computation will be discussed; evolutionary computation theory, evolutionary optimisation and evolutionary learning. The state-of-the-art and open issues in each area will be addressed. It is indicated that while evolutionary computation techniques have enjoyed great success in many engineering applications, the progress in theory has been rather slow. This paper also gives a brief introduction to parallel evolutionary algorithms. Two models of parallel evolutionary algorithms, the island model and the cellular model, are described. 1 Introduction The field of evolutionary computation has grown rapidly in recent years [1, 2, 3]. Engineers and scientists with quite different backgrounds have come together to tackle some of the most difficult problems using a very promising set of stochastic search algorithms --- evolutionary algorithms (EAs). There are several diffe...

This work presents some general procedures for computing dissimilarities between elements of a database or, more generally, nodes of a weighted, undirected, graph. It is based on a Markov-chain model of random walk through the database. The model assigns transition probabilities to the links between elements, so that a random walker can jump from element to element. A quantity, called the average first-passage cost, computes the average cost incurred by a random walker for reaching element k for the first time when starting from element i.

In this paper we introduce a new notion of traversal sequences that we call exploration sequences. Exploration sequences share many properties with the traversal sequences defined in [AKL+], but they also exhibit some new properties. In particular, they have an ability to backtrack, and their random properties are robust under choice of the probability distribution on labels. Further, we present extremely simple constructions of polynomial length universal exploration sequences for some previously studied classes of graphs (e.g., 2-regular graphs, cliques, expanders), and we also present universal exploration sequences for trees. Our constructions beat previously known lower-bounds on the length of universal traversal sequences. 1

This paper uses Markov chains to analyze the search quality of a bounding case of parallel genetic algorithms with multiple populations. In the bounding case considered here, each population exchanges individuals with all the others. First, the migration rate is set to the maximum value possible, and later the analysis is refined to consider lower migration rates. In the algorithm examined by this paper, migration occurs only after each population converges. Then, incoming individuals are incorporated into the populations and the algorithm restarts. The analysis shows how to calculate the probability that each population will eventually converge to the correct solution, and the expected number of migration-restart events until all the populations converge to the same solution.

this paper, we are mainly concerned with the characterization of the fundamental matrix Z(") of the perturbed chain. In the case of a singular perturbation, Z( ) also has a discontinuity at = 0. Moreover, in this case, jjZ(")jj !1 as " ! 0 and Z(") admits a Laurent series expansion [132, 134, 66, 67] Z(") = 1 " s Z s + ::: + 1 " Z 1 + Z 0 + "Z 1 + :::; " 6= 0: (3.47) Note that s, the order of the pole, is nite and s N . We denote the singular and the regular parts of the fundamental matrix expansion (3.47) by Z S (") and Z R ("), respectively. Schweitzer has also obtained formulae for the matrices Z k . However, they are rather complicated and their computation requires to handle large size matrices (cf. [132]). In sequel, we propose a di erent approach that allows us to compute more eciently the coecients of the Laurent series (3.47). This approach can be considered as a particular realisation of the general scheme proposed in Section 2.4 for the perturbation analysis of group inverses. Our method leads to the operations with matrices of small dimensions. For example, immediately after the rst stage of the reduction process one handles aggregated Markov chains with no more than m states (m being the number of ergodic classes). This would, typically, constitute a drastic reduction of the dimension. In addition, for the case of a linear perturbation we provide a simple formula for the regular part Z R ( ), which readily simpli es to the usual formula [131] if the perturbation is regular. We introduce the deviation matrices (or reduced resolvents) H and H(") for the original and perturbed chains: H def = Z P and H(") def = Z(") P ("): We immediately have H S (") = Z S (") and H R (") = Z R (") P ("): (3.48) The fundamental matri...

In this paper we present a new approach to the formal specification of distributed real-time systems using the formal description technique LOTOS together with a stochastic temporal logic STL. This approach previously presented in the context of LOTOS/QTL, is characterized by a separation of concerns. The functional behaviour is described in LOTOS without regard for the time critical constraints. The specification is then extended with precise real-time requirements written in STL. We present a method to generate a timing event scheduler from the requirements in order to monitor the functional behaviour. 1 Introduction Over the past few years there have been several techniques used for the design and the validation of distributed systems. Traditionally, these techniques fall into two distinct fields: qualitative validation and quantitative evaluation. The former field is concerned by the formal correctness of the system and usually employs formal description techniques. These techni...

. In this paper we consider the sequence of consecutive powers of a matrix in a Boolean algebra. We characterize the ultimate behavior of this sequence, we study the transient part of the sequence and we derive upper bounds for the length of this transient part. We also indicate how these results can be used in the analysis of Markov chains and in max-plus-algebraic system theory for discrete event systems. Key words. Boolean algebra, Boolean matrices, transient behavior, Markov chains, max-plus algebra AMS subject classications. 06E99, 15A99, 16Y99 1. Introduction. In this paper we consider the sequence of consecutive powers of a matrix in a Boolean algebra. This sequence reaches a \cyclic" behavior after a nite number of terms. Even for more complex algebraic structures, such as the max-plus algebra (which has maximization and addition as its basic operations) this ultimate behavior has already been studied extensively by several authors (See, e.g., [1, 9, 13, 26] and the refere...

Parallel computing is becoming increasingly accessible through advancement in microprocessors and networking technologies. It is found that the performances of the clusters do not match with their promises, although they are built on the most advanced components. Much effort has been devoted to address the software overhead problem in the past, which is known as the major hindrance in achieving high performance. This thesis shows that having a low-latency communication system does not guarantee high performance, as there are other communication issues that have not been addressed by the use of low-latency communication, such as contention, communication patterns and scheduling of communication events. The development of an efficient parallel application depends upon a realistic prediction of application behavior and the ability to explain the performance characteristics of an application on a parallel system; this requires in-depth understanding of both the application and the architecture characteristics. This dissertation proposes the use of a realistic communication model to guide the performance understanding and the algorithm design processes, which are the keys to

We previously introduced and analyzed the Gt/Mt/st +GIt many-server fluid queue with time-varying parameters, intended as an approximation for the corresponding stochastic queueing model when there are many servers and the system experiences periods of overload. In this paper we establish an asymptotic loss of memory (ALOM) property for that fluid model; i.e., we show that there is asymptotic independence from the initial conditions as time t evolves, under regularity conditions. We show that the difference in the performance functions dissipates over time exponentially fast, again under the regularity conditions. We apply ALOM to show that the stationary G/M/s + GI fluid queue converges to steady state and the periodic Gt/Mt/st + GIt fluid queue converges to a periodic steady state as time evolves, for all finite initial conditions.

Abstract. Metric coinduction is a form of coinduction that can be used to establish properties of objects constructed as a limit of finite approximations. One proves a coinduction step showing that some property is preserved by one step of the approximation process, then automatically infers by the coinduction principle that the property holds of the limit object. This can often be used to avoid complicated analytic arguments involving limits and convergence, replacing them with simpler algebraic arguments. This paper examines the application of this principle in a variety of areas, including infinite streams, Markov chains, Markov decision processes, and non-well-founded sets. These results point to the usefulness of coinduction as a general proof technique. 1