On alternative mixed integer programming formulations and LP-based heuristics for lot-sizing with setup times

We address the multi-item, capacitated lot-sizing problem (CLSP) encountered in environments where demand is dynamic and to be met on time. Items compete for a limited capacity resource, which requires a setup for each lot of items to be produced causing unproductive time but no direct costs. The problem belongs to a class of problems that are difcult to solve. Even the feasibility problem becomes combinatorial when setup times are considered. This difculty in reaching optimality and the practical relevance of CLSP make it important to design and analyse heuristics to nd good solutions that can be implemented in practice. We consider certain mixed integer programming formulations of the problem and develop heuristics including a curtailed branch and bound, for rounding the setup variables in the LP solution of the tighter formulations. We report our computational results for a class of instances taken from literature

Conceptual design of an e-marketplace for small and medium enterprises in the Turkish machinery industry

This paper reports on the results of a study carried out in the Turkish machinery industry. The purpose of the study was to identify the benefits the sector can seize from e-business and to develop a conceptual framework for potential e-business applications. We analysed the current state of e-business use in the machinery industry in order to understand the future requirements and application opportunities and to come up with a conceptual e-business design that would suit both the needs and the characteristics of the sector. The study included those companies, which are members of the Machine Manufacturers’ Association (MMA) in Turkey. Information about the existing applications and future requirements was obtained from the results of a survey conducted among the member companies. Statistically adequate number of responses was obtained to make the results representative of the machine industry. Web sites of the member companies were also reviewed for further information gathering. Results indicated that most of the companies are Small and Medium Enterprises(SME) and it would be better for them to carry out certain operations through an e-market specifically designed for the sector. The proposed conceptual e-market design is based on the characteristics of the industry emerging from the survey

Bilateral control: a sliding mode control approach

Bilateral control is bi-directional control of force-position between two systems connected by a communication link. It is typically used for teleoperation with forcefeedback, such that the master system is handled by an operator. Motions of the operator are fed forward to the slave system, generally remote to the operator and forces encountered are fed back to the master system, enabling a telepresence of the operator in the remote environment. The necessity of bilateral control lies in its applicability to the tasks that cannot be handled by autonomous manipulators and/or reached by human beings. Main issues of consideration for bilateral control, namely transparency, scaling and time delay, are addressed and two discrete-time sliding-mode approaches are presented as solutions to highly transparent bilateral controllers that support scaling. First approach has a force-hybrid architecture, where the cascaded sliding mode hybrid force/position controller on the slave side reacts to the external forces directly. Therefore, it provides a protection (reflex) mechanism on the slave side to large external forces, that the operator cannot respond in time due to the time delay. Second approach has a decentralized nature. Virtual systems are devised by a linear transformation from the plant space to the task space and sliding mode control has been applied to those virtual systems, hence sides of bilateral control are interchangable. The decentralized structure of the controller makes it possible to generalize the problem to a coordination and/or cooperation of more than two plants. High precision has been achieved on experiments for both approaches designed and discussed in detail

Propuesta de un planeamiento tributario en la empresa Productos Dulcinea E.I.R.L., San Luis, 2018

El alcance de esta investigación es mostrar a la empresa Productos Dulcinea E.I.RL. la propuesta de un planeamiento tributario como una estrategia para optimizar su carga tributaria con las diferentes alternativas que nos plantea las normas legales además de conocer qué tipo de contingencias tributarias se encontraría afecta si no obedece los parámetros establecidos por la Administración tributaria y no menos importante para estar preparados ante una fiscalización de la SUNAT. El presente estudio se ha centrado en primer lugar a analizar la situación tributaria de la empresa a través de cuestionarios, la recolección y revisión de la información tanto contable como tributaria sobre el ejercicio 2017, lo cual se ha percibido algunas deficiencias que generó un impacto en la rentabilidad de la empresa, se pudo constatar dicha información a través de una simulación que se realizó para el año 2017, siendo de ese modo la idea de aplicar un planeamiento tributario. La propuesta consiste en 4 componentes, realizar un planeamiento sobre ingresos, gastos, impuesto y la búsqueda de beneficios fiscales, estos componentes van a determinar un ahorro fiscal además de poder contribuir en el rendimiento económico de la empresa para que continúe compitiendo en el mercado

Sliding Modes in Motion Control Systems

In this paper we discuss the realization of motion control systems in the sliding mode control (SMC) frame- work. Any motion control system design should take into account the unconstrained motion (generally perceived as a trajectory tracking) and motion of the system in contact with unknown environment (perceived as force con- trol and/or compliance control.) In the SMC framework control is selected to enforce certain preselected depend- ence among system coordinates, what is interpreted as forcing the system state to stay in selected manifold in state space. ln this paper it has been shown that such a formulation allows a unified treatment of the both un- constrained and constrained motion control and, due to the Lyapunov based design, it guaranty the stability of the motion. Moreover control design in this framework allows extension of the solution to control design in in- terconnected dynamical systems (like mobile robots or bilateral systems)

On the equivalence of strong formulations for capacitated multi-level lot sizing problems with setup times

Several mixed integer programming formulations have been proposed for modeling capacitated multi-level lot sizing problems with setup times. These formulations include the so-called facility location formulation, the shortest route formulation, and the inventory and lot sizing formulation with (l,S) inequalities. In this paper, we demonstrate the equivalence of these formulations when the integrality requirement is relaxed for any subset of binary setup decision variables. This equivalence has significant implications for decomposition-based methods since same optimal solution values are obtained no matter which formulation is used. In particular, we discuss the relax-and-fix method, a decomposition-based heuristic used for the efficient solution of hard lot sizing problems. Computational tests allow us to compare the effectiveness of different formulations using benchmark problems. The choice of formulation directly affects the required computational effort, and our results therefore provide guidelines on choosing an effective formulation during the development of heuristic-based solution procedures

A priori reformulations for joint rolling-horizon scheduling of materials processing and lot-sizing problem

In many production processes, a key material is prepared and then transformed into different final products. The lot sizing decisions concern not only the production of final products, but also that of material preparation in order to take account of their sequence-dependent setup costs and times. The amount of research in recent years indicates the relevance of this problem in various industrial settings. In this paper, facility location reformulation and strengthening constraints are newly applied to a previous lot-sizing model in order to improve solution quality and computing time. Three alternative metaheuristics are used to fix the setup variables, resulting in much improved performance over previous research, especially regarding the use of the metaheuristics for larger instances

Drift or shift? Continuity, change, and international variation in knowledge production in OR/MS

With the aim of contributing to the debate around OR/MS as a discipline, this study provides a historical comparative investigation of publicly available knowledge production in the field. The empirical investigation is based on a content analysis of 300 randomly selected articles from six major journals in the field. We have found: (1) since the late 1950s to the present day there has been no significant change in the types of published research in OR/MS in North America; (2) from the late 1950s to the present day, there have been significant differences in types of published research in OR/MS internationally. The imputed imbalance between theory and applications in published work had already occurred in the early stages of the development of OR/MS in North America and has since remained very much the same. Furthermore, research in the United Kingdom has been distinctly different from that dominant in North America and elsewhere. There are also indications that outside North America and the United Kingdom there is an emerging turn towards applications-oriented research. Over the last two or three decades there has been a significant increase overall in the share of articles published by academic authors