Sharif Digital Repository

In this thesis, a decomposition approach is developed to solve Set Covering Problems (SCPs) through exploiting special structures of their coefficient matrices. The coefficient matrix of an SCP is so large in practical problems, but due to its low density, most of its entries are zero. Based on this observation, some methods can be developed to aggregate the 1's of the coefficient matrix in order to create special structures involving smaller dense subproblems. In this theisis, four structures called "block-angular", "semi-block angular", "partitioned" and "nested block-angular" structures are proposed and examined. For this purpose, First, some heuristic methods based on constraint... 

The human need for reliable and accessible energy sources for household, industrial, transportation, etc. caused the discovery of the first oil well to move towards exploitation and use of this large, cheap and available energy source, accelerated. With the start of this movement, oil and its products in the last two centuries have quickly established themselves as a major part of the energy basket of most countries in the world. The entry of crude oil and its products into the energy industry has faced new issues and challenges for decision makers in this field. One of the most important challenges has been the planning and management of the process of distribution and transfer of petroleum... 

The subgradient method is one of the most favoriate methods to solve discrete optimization problems. The Easy Implementation and flexibility enbles us to solve a vast types of complicated combinatorial optimization problems. However, the algorithm can be improved by adjusting its parameters and steps.In present research, we present a heuristic structure to modify and improve the algorithm. Then, the proposed algorithm has tested on special classes of discrete optimization problems such as Generealized Assignment and Uncapacitated Warehouse location problems. The results show that the proposed algorithm can improve the efficiency of the classic form of subgradient method.The three main... 

Subgraph isomorphism problem is an NP-complete problem, which has diverse applications in different fields such as network problems, image processing, text processing, topography, and bioinformatics. Therefore, many researchers from both theoretical and practical viewpoints have considered it. In this research, we try to offer a proper and efficient method to solve this problem by using constraint programming, which is a powerful and efficient method to model and solve complicated combinatorial optimization problems, and criticality and cruciality concepts from a resource planning scope.
In this regard, first one of the most efficient models among existing constraint programming models... 

One of the newest approaches in optimization fields under uncertainty which absorb many scientists is robust optimization. This approach uses uncertain data instead of stochastic distributions and its goal is to find a solution which is robust under uncertainty of input data.
Assignment problem is one of the most applicable problems in real world which its parameter is faced uncertainty. Because of this reason, the aim of this thesis is to find a method for solving generalized assignment problem robustly which the coefficients of costs and use of resources by agents for performing the jobs is undetermined. These parameters are interval data and have just lower and upper bound.
For... 

In complex human social activities, practical problems involve more prominent uncertainty, and deterministic approaches of classical methods become powerless. In this research, a new method for human group decision making is presented by using heterogeneous incomplete uncertain preference relations. The uncertain multiplicative preference relations, uncertain fuzzy preference relations, uncertain linguistic preference relations, intuitionistic fuzzy preference relations and Interval
preference sequence can be included in this method.Our new method consists of nine steps. In the first step, decision-makers preferences in the form of heterogeneous comparison matrixes are driven.In the... 

Wireless sensor networks have been widely used in such areas as intelligent transport systems, military systems and etc. Wireless sensor networks are composed of a number of sensor nodes in charge of data collection, analysis and transport. The energy limitations on wireless sensors have brought researchers to work on algorithms intended for efficient use of energy and therefor maximum network life.
In this work, we will first present a detailed description of two well-known protocols: LEACH and AODV. In the second part, an optimized routing protocol for wireless networks, based on the previously described protocols and the ant colony theory will be presented. The optimized protocol will... 

One of the primary concerns on many traditional capacitated facility location-network design problems is to consider costs of transportation and establishing of facilities in one single objective function. Considering a single objective in these problems may lead to misleading solutions due to the fact that the transportation costs should be considered in a short-term period of time, and therefore, the higher cost of establishing the facilities may unfairly dilute the role of the transportation cost. In this thesis, we introduce the capacitated facility location-network design problem with two separate objective functions. Moreover, in this problem, it is assumed that for connecting two... 

Breast cancer has been one of the main causes of women's deaths in recent years. Today, various methods are used to treat this disease, among which intensity-modulated radiation therapy is one of the most common methods. The goal of radiation therapy is to destroy cancer cells while protecting the surrounding healthy tissues. In left breast cancer, due to the proximity of the heart and breast tissue, we are at risk of delivering an excessive dose to the heart and increasing cardiac complications after the treatment. In addition, due to the irregular and unpredictable breathing movements of the patient during the treatment and the resulting uncertainty, we face more challenges. In order to... 

In this study, providing home care services by hospitals in the epidemic situations such as COVID-19 is proposed for the first time. Moreover, a mathematical formulation is developed to provide simultaneous decision-making about serving patients without COVID-19, scheduling nurses in the non-COVID-19 wards of hospitals, and scheduling and routing for nurses to serve patients at home. This problem aims to develop essential compatibilities to keep people safe and help continue vital healthcare services during the COVID-19 and similar pandemics. Accordingly, nurses' preferences, the number of available hospital beds, the patient-to-nurse ratio, the Unavailability of some nurses due to COVID-19,... 

In this research, we try to coordinate a seller-buyer supply chain by using general side-payment contracts in order to gain the maximum possible chain profit. In this model, we take logistics costs into consideration for both buyer and seller and regard the final demand as a decreasing function of retail price which is determined by the buyer. Both parties aim to maximize their individual profits, so we must set contractual parameters in a way that these decisions become aligned with system optimal decisions and the chain surplus profit be assigned to chain members such that they have no intention to leave the coalition. To this aim, we suggest a side- payment contract which consists of... 

Layout design problem is to determine a suitable arrangement for the departments, so that the total costs associated with the flow among departments become least. Single Row Facility Layout Problem which is called SRFLP, is one of layout problems that has many practical applications. This problem and its specific scenarios is often used to model many of the raised issues. This is arrangements of n departments with a specified length in a straight line, so that the sum of the weighted distances between pairs of departments is minimized. We can say that SRFLP is one-dimensional version of the layout design problem and it tries to minimize the cost of communication between rectangular... 

Search engines have an important role in providing the appropriate response to the user’s search. In the past, all people had received the same result for searching an equal expression. Now, no one receives a similar answer by searching in Google or Bing. The information in the net is getting bigger day by day. Thus, websites owners face a serious challenge to provide a suitable and relevant information for the users. Accordingly, ranking the results for users is difficult. To address this issue, researchers proposed different ranking algorithms for sorting the search results. Travel and tourism is one of the most competitive and cost-consuming in the field of electronic commerce especially... 

In this thesis, a special case of the Traveling Purchaser Problem (TPP) is considered in which instead of one vehicle there are multiple vehicles as purchasers. Furthermore, the vehicles start their path from a set of starting points and after visiting a number of markets they return to the depot. Moreover, each of the products needs a special loading condition and the vehicles have multiple compartments to meet these loading constraints and the products are loaded in their appropriate compartments. This problem is at first modeled as a MIP formulation and then by decomposing the problem a Column Generation procedure is developed to solve the problem. To enhance the speed of the column...