Journal of Operational Research in its Applications
Year:2018 | Volume:15 | Issue:2 (57) |Papers Count:9

In this paper, mean absolute deviation model for optimal portfolio selection problem is studied. Due to the uncertainty in the observed returns from financial markets, an improved robust formulation based on Bertsimas and Sim approach is presented. Then we study the robust model of the problem under correlated uncertainty set and give its equivalent model. Finally, the performance of the improved and correlated robust models is compared with the original one on real data from financial markets.

Increasing the production level of manufacturing systems, which is an undesirable outcome of industrial development, has grown increasingly in recent years. The negative effects of this event have caused companies to make decisions for implementing environmental management in order to maintain their position. Among these decisions is considering the green issues in supply chain, which is largely influenced by performance of their suppliers. Therefore, evaluation and selection of green suppliers is a strategic decision for attendance in competitive markets and retaining companies' social position. Due to the variety of evaluation criteria, being quantitative or qualitative and the fuzzy nature of qualitative criteria, this research proposed a hybrid fuzzy MCDM approach based on fuzzy Delphi, fuzzy analytical hierarchy process and Fuzzy VIKOR for evaluating and selecting the green suppliers of Saipa Company. To this aim, first by reviewing the theoretical literature, supplier selection criteria in green supply chain were explored. Then, by examining the current status of Saipa company, consulting with the experts and using the fuzzy Delphi method, more important criteria were identified. In the next step, the final criteria were distributed among companies’ experts in form of a paired comparison questionnaire, and the necessary data for prioritization of the criteria based on the technique of the fuzzy analytical hierarchy process, were collected. Finally, 100 suppliers of the Saipa company were evaluated using fuzzy VIKOR technique. The results indicated that the proposed approach is an effective framework for prioritizing the green suppliers of Saipa Company.

Increasing the production level of manufacturing systems, which is an undesirable outcome of industrial development, has grown increasingly in recent years. The negative effects of this event have caused companies to make decisions for implementing environmental management in order to maintain their position. Among these decisions is considering the green issues in supply chain, which is largely influenced by performance of their suppliers. Therefore, evaluation and selection of green suppliers is a strategic decision for attendance in competitive markets and retaining companies' social position. Due to the variety of evaluation criteria, being quantitative or qualitative and the fuzzy nature of qualitative criteria, this research proposed a hybrid fuzzy MCDM approach based on fuzzy Delphi, fuzzy analytical hierarchy process and Fuzzy VIKOR for evaluating and selecting the green suppliers of Saipa Company. To this aim, first by reviewing the theoretical literature, supplier selection criteria in green supply chain were explored. Then, by examining the current status of Saipa company, consulting with the experts and using the fuzzy Delphi method, more important criteria were identified. In the next step, the final criteria were distributed among companies’ experts in form of a paired comparison questionnaire, and the necessary data for prioritization of the criteria based on the technique of the fuzzy analytical hierarchy process, were collected. Finally, 100 suppliers of the Saipa company were evaluated using fuzzy VIKOR technique. The results indicated that the proposed approach is an effective framework for prioritizing the green suppliers of Saipa Company.

In this paper we consider the reverse backup 2-median problem with variable coordinates of vertices in Rk. Let n points be given, then in the reverse backup 2-median problem we want to change the coordinates of these points with a limited budget such that the two given points become the backup 2-median. We present a mathematical model for this problem and then solve a spatial case of this problem by a meta-heuristic method.

The most important issue for investors in stock exchange is how to select appropriate stock in order to achieve most yields. So financial performance evaluation of companies can help investors in investment appropriate decision making. One of the performance evaluation methods is ranking companies stock according to different financial criteria. This research uses Integrated Fuzzy Logarithmic Preference Programming method in order to rank companies stock of "multiple fields industry". The mentioned method is a two-step nonlinear programming model that extracts relative importance degree of the companies’ stock and performance evaluation criteria from fuzzy paired comparison matrix. Findings of the research shows that the stock of Tosey-e-Melli group investment company has had the best performance and the stock of Omid investment company has had the worst performance during the performance evaluation period (year 1395). Moreover, according to the views of analysts and experts of the capital market, the criteria "Earning Per Share" and "P/E" have the most effect on performance evaluation of the companies’ stocks. According to the achieved results, it’s recommended that this method should be used in order to invest portfolio construction at a greater level. Moreover, it’s necessary that different investors for companies’ stock analysis consider more about the criteria of "Earning Per Share" and "P/E".

Companies with sustainable development and competitive advantage goal, need to consider suppliers as a part of their own core competencies. Accordingly, supplier selection should be considered as an important part of the strategic decisions of these kinds of companies. Supplier selection is usually formulated as a multi criteria decision making problem. When suppliers are selected, it is essential to solve order allocation problems that means determining the amount of order for each selected supplier. So, solving supplier selection and order allocation with integrated model as a research area, has attracted many attentions. According to experience of previous researches, formulating integrated model for solving these two problems leads to a multi-objective mix integer program. Assuming available delivery time data as a sample of real behavior of suppliers, this paper improved a practical aspect of formulation of this problem by utilizing sampling distribution concept. A simple but relatively different solution method that guarantees at least one optimum objective is applied as well.

There have been many methods for ranking of DMUs so far. Some of the previous proposed methods may be infeasible and others cannot rank all DMUs. In this paper, we introduce a new method for ranking of DMUs that is always feasible and can be used for ranking of all DMUs. The rank of DMUs is achieved based on ideal hyper planes. The sensitivity of the ranks is presented as well. Therefore, in this study, a stability interval is proposed for the ranks. Finally, a numerical example is given.

Gas refineries are one of the pivotal industries, which have a crucial role in economic development of countries. Because of such an importance, a rich literature in evaluating and ranking these organizations can be found. Data envelopment analysis is a popular non-parametric technique that has received much attention in the mentioned area. The current research, using two-stage CCR based data envelopment analysis technique, aims at evaluating 11 gas refineries in Iran between 1392-1394. In this regard, numerical results show that some of the refineries lie on the efficient frontier; Hence, Anderson-Peterson method is employed to rank the efficient ones, and this way phases 9 and 10 of ASALUYE refinery are introduced as the strong efficient DMUs. Malmquist index has also been applied to investigate the progression/ retrogression of the DMUs.