Annals of Optimization Theory and Practice
Volume:1 Issue: 3, Autumn 2018

In this study a non-linear weighted sum model is proposed to rank countries based on economic factors. This ranking problem could be new and useful as most of previous researches rated countries not rank them. The countries are ranked from the best to the worst one by their score obtained by the model from credit point of view. As an advantage of the model, it is solvable by an analytical solution method manually instead of using optimization software. The analytical solution is useful for managers and decision makers to apply the model easily. The obtained ranking is compared with Moody’s rating to discuss the efficiency of the model.

Flexible robotic cells are used in many real-life industries to produce standardized items at a high production speed. Determining the schedules of these cells is an important optimization problem in those industries. In this study, the cell's machines are identical and parallel. In the cell, there is an input and an output buffer wherein items being processed and the finished items are kept, respectively. There is a robot performing the loading/unloading operations of the machines and transporting the items. The system repeats a cycle in its run. Each machine processes one part in each cycle. The cycle time depends on the order of the loading/unloading activities. Therefore, determining the order of these activities for the minimum cycle time is needed. We propose a new mathematical model to solve the problem. For large size problems, three metaheuristic algorithms based on local search algorithm are proposed. In the metaheuristics, in order to compute the minimum cycle time of a given solution a linear programming model is needed to be solved which is one of the recent cases in the literature to the best of our knowledge. Several numerical examples are solved by the proposed algorithms and their performance and solutions are compared.

Considering the importance of customers' loyalty and the existing competitive environment, it is necessary to assess the factors affecting customer loyalty to find out the levels of effectiveness of different factors on customer' loyalty and the performance of different stores in this field. Therefore, in this research, a model is provided to rate the customer loyalty levels of grocery stores in the Ahvaz city with ANP and TOPSIS mixed approach. Different stages of the presented model include designing the conceptual model of the effective factors on loyalty of the customers of grocery stores, measuring the weights of the factors using ANP and rating the performances of the stores using TOPSIS. The results show that pricing is the most important factor when it comes to customer loyalty and after that quality of the goods, quality of the services, variety and innovation and technology are the most important factors in customer loyalty, respectively. Also the best performance by a grocery store is determined.

In this paper, we explain the rumor spreader model with a differential equation system and analyses and consider this system in dynamical system view. The model which we consider in a society contains ignoring, spreading, stifle and controlling factors. In this work, we study on a new rumor spreading model, Ignorant-Spreader-Stifler-Controller (ISRC) model, is developed. The model extends the classical Ignorant-Spreader-Stifler (ISR) rumor spreading model by adding a new kind of people that spread a new rumor against previous rumor to control and reduce the maximum rumor influence.The model is an extension of SIR model which has studied before. In this research, we give a dynamical system which explains SIRC dynamical factors. Moreover, we consider the equilibrium conditions near the equilibrium point.