Multiparametric sensitivity analysis in programming problem with linear-plus-linear fractional objective function

In this paper, we study multiparametric sensitivity analysis for programming problems with linear-plus-linear fractional objective function using the concept of maximum volume in the tolerance region. We construct critical regions for simultaneous and independent perturbations in the objective function coefficients and in the right-hand-side vector of the given problem. Necessary and sufficient conditions are derived to classify perturbation parameters as `focal' and `non-focal'. Non-focal parameters can have unlimited variations, because of their low sensitivity in practice, these parameters can be deleted from the analysis. For focal parameters, a maximum volume tolerance region is characterized. Theoretical results are illustrated with the help of a numerical example.     

A new method of digital simulation for an aircraft gas turbine engine control system

An LD-9 aircraft gas turbine engine with its control system is simulated digitally by a new method, called the ‘method of spare parts’. The computer program of simulation possesses the main capabilities of a real engine altitude test facility and is called a ‘digital engine altitude simulator’. The results of simulation show that the capabilities of this new method are much better than that of the ordinary ‘method of block diagram’. The method can be used for modelling and simulating any type of gas turbine engines or industrial process control systems.     

Sequences with idempotent products from finite regular semigroups

We find the smallest integer (n) such that for every regular semigroup S of order n, every sequence of length (n) of elements of S contains a consecutive subsequence whose product is an -element, where = ‘idempotent’, ‘core’ and ‘subgroup and core’. For arbitrary semigroups of order n, we also find (n) where = ‘regular’, ‘group’, ‘core’, ‘regular and core’ and ‘subgroup and core’.     

On arithmetic properties of integers with missing digits II: Prime factors

Prime factors of numbers with missing digits are studied. It is shown that, under certain conditions, this set satisfies an Erd s-Kac type theorem; it contains numbers with ‘many’ prime factors; it contains numbers whose greatest prime factor is ‘large’ (resp. ‘small’).     

A unified approach for price directive decomposition procedures in integer programming

This paper shows how to generalize the Dantzig-Wolfe decomposition principle to integer programming. It does this in a unified way, regardless of the choice between the two main solution methods: ‘Branch and bound’ or ‘cutting plane’. In both instances the authority at the central level issues price directives in the form of a polyhedral, concave price function, where the purpose is to charge the sublevels for the use of central resources including a penalty for any attempts to violate the integrality of the result. The sublevels then respond with their optimal activities given this price function. Finite convergence of the procedure is established.     

Topology optimization of periodic Mindlin plates

Periodic structures exhibit unique dynamic characteristics that make them act as tunable mechanical filters for wave propagation. As a result, waves can propagate along the periodic structures only within specific frequency bands called the ‘pass bands’ and wave propagation is completely blocked within other frequency bands called the ‘stop bands’ or ‘band gaps’. The spectral width of these bands can be optimized using topology optimization. In this paper, topology optimization is used to maximize the fundamental natural frequency of Mindlin plates while enforcing periodicity. A finite element model for Mindlin plates is presented and used along with an optimization algorithm that accounts for the periodicity constraint in order to determine the optimal topologies of plates with various periodic configurations. The obtained results demonstrate the effectiveness of the proposed design optimization approach in generating periodic plates with optimal natural frequency and wide stop bands. The presented approach can be invaluable design tool for many structures in order to control the wave propagation in an attempt to stop/confine the propagation of undesirable disturbances.     

From greedy to lazy expansions and their driving dynamics

In this paper we study the ergodic properties of non-greedy series expansions to non-integer bases β > 1. It is shown that the so-called ‘lazy’ expansion is isomorphic to the ‘greedy’ expansion. Furthermore, a class of expansions to base β > 1, β , ‘in between’ the lazy and the greedy expansions are introduced and studies. It is shown that these expansions are isomorphic to expansions of the form Tx = βx + (mod 1).     

Soliton chaos and lengthscale competition in nonlinear dynamics

Perturbing soliton-bearing completely integrable dynamics can give rise to rich and fascinating behaviour. If the perturbation introduces a lengthscale which is large compared to the spatial extent of the solitons present in the system, the solitons move like particles in an effective potential. Taking into account two-soliton interaction can result in chaotic behaviour called ‘soliton chaos’. In the opposite limit of a small-lengthscale perturbation the solitons acquire a dressing which effectively shields them from the perturbation. If the resulting ‘dressed solitons’ are subject to an additional long-wavelength perturbation they move like renormalised particles. Furthermore they can scatter nearly elastically. If the perturbation contains lengthscales which are comparable to one of the soliton's typical lengthscales then lengthscale competition can occur. Neither the particle approximation nor the dressed-particle approximation for the soliton is valid and complicated spatio-temporal behaviour is observed. We illustrate this scenario by means of the perturbed nonlinear Schrödinger equation. The perturbed sine-Gordon equation and the Ablowitz-Ladik equation are also discussed.     

An arithmetic proof of John’s ellipsoid theorem

Using an idea of Voronoi in the geometric theory of positive definite quadratic forms, we give a transparent proof of John’s characterization of the unique ellipsoid of maximum volume contained in a convex body. The same idea applies to the ‘hard part’ of a generalization of John’s theorem and shows the difficulties of the corresponding ‘easy part’.Received: 8 October 2004     

Composite mix design in the production of asbestos/cement pipes

A mathematical model is presented for the determination of optimal mix of asbestos fibres to satisfy a set of desired pipe properties which vary with pipe size, class, and material availability. The approach utilizes a linear/separable programming model which is aimed at minimizing the total cost of fibres used. The fibre properties, such as reinforcing strength, processability, and length as well as cost and stocks available are taken into account in the model. Also represented are the profile of the ideal mix relative to the required composite strength, processability, and ‘dust content’. Asbestos mixes designed using the model have been implemented in the production of asbestos/cement pipes in one of the asbestos/cement pipe manufacturing plants in the Gulf area. Optimum model mixes have demonstrated significant technical and economic merits over the conventionally designed mixes.     

Enhancing the generality of fuzzy relational models for control

A promising area of research in fuzzy control is the model-based fuzzy controller. At the heart of this approach is a fuzzy relational model of the process to be controlled. Since this model is identified directly from process input-output data it is likely that ‘holes’ will be present in the identified relational model. These holes are real problems when the model is incorporated into a model-based controller since the model will be unable to make any predictions whatsoever if the system drifts into an unknown region. The present work deals with the completeness of the fuzzy relational model which forms the core of the controller. This work proposes a scheme of post-processing to ‘fiil in’ the fuzzy relational model once it has been built and thereby improve its applicability for on-line control. A comparative study of the post-processed model and conventional relational model is presented for Box-Jenkins data identification system and a real-time, highly non-linear application of pH control identification.     

What is sustainable development? An attempt to interpret it as a soliton-like phenomenon

An attempt is made to establish a relation between the question of what ‘sustainable development’ means and the non-linear theory of shock waves. Despite the presence of dispersive, i.e. entropy-producing, forces a soliton-like, isentropic, transport of a wilfully desired distribution in a field of traded commodities is possible. Starting with the classical Korteweg de Vries (KdV) equation, two other examples, a sigmoidal and a Gaussian soliton in a diffusional environment, are analyzed in detail as a guide-line of how a ‘sustainable’ transport of an economically defined creation can be carried through time.     

An introduction to hierarchical displacement elements and the adaptive technique

The ‘adaptive technique’ is the capability for re-analysis with a minimum of additional data preparation and user interaction and is based on a special finite element formulation which is referred to as the ‘hierarchical formulation’. This paper gives an introductory insight into this newly emerging commercial capability and concentrates on displacement-based elements.     

An integrative approach to 2D-macromodels of growth, price and inventory dynamics

This paper investigates two variants of a Keynesian model of monetary growth with sluggish price and quantity adjustments. The first model integrates the real growth dynamics of Rose's employment cycle, an inflationary dynamics of the Cagan type and Metzler's inventory dynamics. This model is based on intrinsic nonlinearities solely and it implies for the private sector six laws of motion, two for each of the subdynamics stated above. It is shown that the integrated model does not at all preserve the insights obtained from the three prototype subdynamics. Since this model can give rise to global instabilities even for moderate adjustment speeds of prices and quantities, a variant of this model is then introduced which exhibits one fundamental ‘nonintrinsic’ nonlinearity in its wage adjustment mechanism. This nonlinearity makes the considered 6D-dynamics at the same time extremely ‘viable’ and complex, in particular for a high adjustment speed of nominal wages.     

Tolerance approach to sensitivity analysis in linear complementarity problems

In this paper, we apply the tolerance approach proposed by Wendell for sensitivity analysis in linear programs to study sensitivity analysis in linear complementarity problems. In the tolerance approach, we find the range or the maximum tolerance within which the coefficients of the right-hand side of the problem can vary simultaneously and independently such that the solution of the original and the perturbed problems have the same index set of nonzero elements.The work of the first author was completed while he was at Virginia Commonwealth University, Richmond, Virginia.     

How to draw a group?

A map is at the same time a group. To represent a map (that is, a graph drawn on the sphere or on another surface) we usually use a pair of permutations on the set of the ‘ends’ of edges. These permutations generate a group which we call a cartographic group. The main motivation for the study of the cartographic group is the so-called theory of “dessins d'enfants’ of Grothendieck, which relates the theory of maps to Galois theory [24].

In the present paper we address the questions of identifying the cartographic group for a given map, and of constructing the maps with a given cartographic group.     

Using bounds on the data in linear programming: The tolerance approach to sensitivity analysis

In contrast to traditional sensitivity analysis in linear programming, the tolerance approach considers simultaneous and independent variations in a number of parameters. A primary focus of this approach is to determine a maximum tolerance percentage for selected right-hand-side terms in which the same basis is optimal as long as each term is accurate to within that percentage of its estimated value. Similarly, the approach yields a maximum tolerance percentage for selected objective function coefficients. This paper shows how the tolerance approach can exploit information on the range of possible values over which terms and coefficients can vary to yield larger maximum tolerance percentages.     

El Naschie’s structures in the electrodynamics of polarizable media

Using the concept of ‘combined field’, an electrodynamics of polarizable media on a fractal space–time is constructed. In this context, using the scale relativity theory, the permanent electric moment, the induced electric moment, the vacuum fluctuations, the paraelectrics, the diaelectrics, the electric Zeeman-type effect, the electric Einstein–de Haas-type effect, the electric Aharonov–Bohm-type effect, the superconductors in the ‘combined field’, the double layers as coherent structures, the magnetic Aharonov–Casher-type effect, are analyzed. Correspondence with the ε^(∞) space–time is accomplished either by admitting an anomal electric Zeeman-type effect, or through a fractal string as in the case of a superconductor in ‘combined field’, or, by phase coherence of the electron–ion pairs from the electric double layers (El Naschie’s coherence). Moreover, the electric double layer or multiple layer may be considered as two-dimensional projections of the same El Naschie’s fractal strings (higher-dimensional strings in ε^(∞) space–time).     

Dynamic spanning without probabilities

The paper presents a non-probabilistic approach to continuous-time trading where, in analogy to the binomial option-pricing model, terminal payoffs resulting from a given trading strategy are meaningful ‘state-by-state’, i.e., path-by-path. In particular, we obtain results of the form: “If a certain trading strategy is applied and if the realized price trajectory satisfies a certain analytical property, then the terminal payoff is.…” This way, derivation of the Black and Scholes formula and its extension become an exercise in the analysis of a certain class of real functions. While results of the above forms are of great interest if the analytical property in question is believed to be satisfied for almost all realized price trajectories (for example, if the price is believed to follow a certain stochastic process which has this property with probability 1), they are valid regardless of the stochastic process which presumably generates the possible price trajectories or the probability assigned to the set of all paths having this analytical property.     

Game Analysis of Investment in a Group with Stickiness

This paper studies the investment in a group with stickiness. A?group investment game is constructed. By analyzing the best response of each player, the equilibria are presented. Furthermore, the convergence region of each equilibrium is outlined, and the sensitivity analysis of the region to parameters is explored. The game with two players is given to illustrate the convergence region of each equilibrium. The explanation and illustration of the results are summarized. The findings indicate that a successful investment usually occurs in a group with ??tolerance??, ??open-sharing??, ??efficiency??, ??sensitivity??, and with large members.