Search results for "Mathematical optimization"
showing 10 items of 1300 documents
An improved method for estimating the frequency correlation function
2012
For time-invariant frequency-selective channels, the transfer function is a superposition of waves having different propagation delays and path gains. In order to estimate the frequency correlation function (FCF) of such channels, the frequency averaging technique can be utilized. The obtained FCF can be expressed as a sum of auto-terms (ATs) and cross-terms (CTs). The ATs are caused by the autocorrelation of individual path components. The CTs are due to the cross-correlation of different path components. These CTs have no physical meaning and leads to an estimation error. We propose a new estimation method aiming to improve the estimation accuracy of the FCF of a band-limited transfer fun…
Methodological Approach to Studying the dynamics of production networks: a Discrete Event Simulation Model
2013
This paper shows how discrete-event simulation represents an appropriate tool for approaching the dynamics of production networks. Three important factors influencing production network dynamics, specifically finite production capacity, manufacturing lead time, and its variability are discussed and a basic discrete-event simulation model is presented. Such model, which in its basic form represents a simple retail/distribution two-stage supply chain, is then extended in order to take into account those factors that can not be included in a classical control theoretical model.
General Economic Order Quantity Model for Lot Sizing with Quality Loss and Process Analysis
1995
In this paper a new model GEOQ is proposed to decide the optimal lot sizing in production. The GEOQ modifies the classical EOQ method in several aspects. First it considers that there is always a probability that the production goes out-of-control; then it takes the time the process goes out-of-control as a stochastic quantity; and finally it adds quality loss to the economic models. The quality loss is calculated according to Taguchi’s quadratic loss function. and depends on the process failure models. Therefore, the optimal lot sizing is decided not only by the set-up cost and the holding cost but also by the quality loss during the manufacturing process.
Context-Independent Scatter and Tabu Search for Permutation Problems
2005
In this paper, we develop a general-purpose heuristic for permutations problems. The procedure is based on the scatter-search and tabu-search methodologies and treats the objective-function evaluation as a black box, making the search algorithm context-independent. Therefore, our main contribution consists of the development and testing of a procedure that uses no knowledge from the problem context to search for the optimal solution. We perform computational experiments with four well-known permutation problems to study the efficiency and effectiveness of the proposed method. These experiments include a comparison with two commercially available software packages that are also based on met…
Incremental bipartite drawing problem
2001
Abstract Layout strategies that strive to preserve perspective from earlier drawings are called incremental. In this paper we study the incremental arc crossing minimization problem for bipartite graphs. We develop a greedy randomized adaptive search procedure (GRASP) for this problem. We have also developed a branch-and-bound algorithm in order to compute the relative gap to the optimal solution of the GRASP approach. Computational experiments are performed with 450 graph instances to first study the effect of changes in grasp search parameters and then to test the efficiency of the proposed procedure. Scope and purpose Many information systems require graphs to be drawn so that these syst…
Heuristics for the bandwidth colouring problem
2010
The bandwidth colouring problem consists of assigning a colour to each vertex of a graph, so that the absolute value of the difference between the colours of adjacent vertices is at least the value of the weight of the associated edge. This problem generalises the classical vertex colouring problem and different heuristics have recently been proposed to obtain high quality solutions. In this paper we describe both memory-based and memory-less methods to solve the bandwidth colouring problem. In particular we propose new constructive and improvement methods based on tabu search and GRASP. Comparison of our results with previously reported instances and existing heuristics indicate that the m…
The Power of the “Pursuit” Learning Paradigm in the Partitioning of Data
2019
Traditional Learning Automata (LA) work with the understanding that the actions are chosen purely based on the “state” in which the machine is. This modus operandus completely ignores any estimation of the Random Environment’s (RE’s) (specified as \(\mathbb {E}\)) reward/penalty probabilities. To take these into consideration, Estimator/Pursuit LA utilize “cheap” estimates of the Environment’s reward probabilities to make them converge by an order of magnitude faster. This concept is quite simply the following: Inexpensive estimates of the reward probabilities can be used to rank the actions. Thereafter, when the action probability vector has to be updated, it is done not on the basis of th…
Duality for constrained multifacility location problems with mixed norms and applications
1989
A dual problem is developed for the constrained multifacility minisum location problems involving mixed norms. General optimality conditions are also obtained providing new algorithms based on the concept of partial inverse of a multifunction. These algorithms which are decomposition methods, generate sequences globally converging to a primal and a dual solution respectively. Numerical results are reported.
Parametric and nonparametric methods to generate time-varying surrogate data.
2009
We present both nonparametric and parametric approaches to generating time-varying surrogate data. Nonparametric and parametric approaches are based on the use of the short-time Fourier transform and a time-varying autoregressive model, respectively. Time-varying surrogate data (TVSD) can be used to determine the statistical significance of the linear and nonlinear coherence function estimates. Two advantages of the TVSD are that it keeps one from having to make an arbitrary decision about the significance of the coherence value, and it properly takes into account statistical significance levels, which may change with time. Our simulation examples and experimental results on blood pressure …
Design of robust observer for T-S fuzzy time-delayed systems subject to unknown inputs
2013
In this paper, a novel approach is proposed to design a robust observer for a class of Takagi-Sugeno (T-S) fuzzy models with unknown inputs and delays. The main contribution of this paper is to consider unknown inputs and a mixed neutral and discrete delay in the model. Also, the system is subject to disturbances, which are imposed on both state and output signals. Delay-dependent sufficient conditions for the design of an unknown input T-S observer with time delays are given in terms of linear matrix inequalities (LMIs). Some relaxations are introduced by using intermediate variables. A numerical example is given to illustrate the effectiveness of the given results.