Aplicação de redes neuronais na previsão de vendas para retalho

Tese de Mestrado Integrado. Engenharia Mecânica. Faculdade de Engenharia. Universidade do Porto. 201

O problema do mercador viajante

O propósito deste trabalho é de dar a conhecer o Problema do Mercador Viajante (Travelling Purchaser Problem – TPP), apresentado-o e resolvendo-o. O TPP tem uma lista de mercados e uma lista de produtos. As distâncias entre mercados são dadas, assim como os preços de cada produto em cada mercado. Pretende-se encontrar um trajeto onde seja possível adquirir todos os produtos, sendo esse trajeto um conjunto ordenado de mercados. O objetivo é encontrar o trajeto mais curto e ao mesmo tempo mais barato, por outras palavras, onde os produtos se adquirem aos seus menores preços. Existem duas grandes dificuldades. A primeira é o facto de o TPP se tratar de um problema pertencente a NP-Hard. A segunda dificuldade reside no facto de se pretender minimizar dois objetivos: a distância e o preço. Esses objetivos entram em conflito um com o outro. Em vez de se procurar uma solução ótima, deve procurar-se uma fronteira de eficiência ótima. Esse tipo de problemas é designado por bi-objetivo, pois ao melhorar-se um objetivo, quase sempre se piora o outro. Sendo assim, mantémse um conjunto de soluções ótimas, onde existem algumas com boas distâncias e outras com bons preços, e apresenta-se esse conjunto como uma fronteira não dominada de soluções. É usado um algoritmo branch and bound para encontrar as fronteiras de soluções ótimas. Aplicam-se alguns cortes básicos no espaço de resultados durante a execução do algoritmo exato para evitar percorrer soluções desnecessárias. É ainda criada uma base de dados de soluções obtidas a partir do algoritmo exato truncado e de um algoritmo de escalada do monte.The purpose of this work is to present and solve the Travelling Purchaser Problem. The TPP has a list of markets and a list of products. The distances between markets are given, and the prices of each product in each market as well. The aim is to find a path where it is possible to buy all the products, and that path being a set of ordered markets. The goal is to find the shortest path and, at the same time, the cheapest one, where the products can be bought at their minimum price among all the markets. There are two major issues. The first one is the fact that the TPP is an NP-Hard problem. The second issue lies in the fact that both objectives should be minimized: the distance and the price. These objectives are in conflict with each other. Instead of searching for an optimal solution, we must search for an optimal efficient front. This kind of problems are referred as bi-objective, because improving one objective, almost always lowers the other. So, we keep a set of optimal solutions, where there are some with good distances and others with good prices, and we present this set as a non dominated front. We use a branch and bound algorithm in order to find the non dominated fronts of optimal solutions. We apply some basic cuts in the search space during the exact algorithm, in order to avoid visiting unnecessary solutions. We create a database of solutions obtained by the truncated exact algorithm and a Hill Climbing algorithm

Symbolic uses of export information: implications for export performance

As export competition becomes more intense and export success vital for survival (Katsikeas, 1994), so the effective processing and use of information regarding the international environment becomes a critical prerequisite for gaining competitive advantage (Leonidou and Theodosiou, 2004). Symbolic use of information is one type of information use, which although relatively underexplored to date, may be the most prevalent form of information use within organisations – especially in an export setting (Beyer and Trice, 1982). Symbolic use occurs when information is used for purposes other than the ones which led to its collection (Menon and Varadarajan, 1992). Symbolic use of information has been conceptualised as a multi-dimensional construct encompassing various dimensions (Vyas and Souchon, 2003). Examples include “exporters that engage in distorting market research findings, taking conclusions out of context, disclosing only the findings that confirm an executive‟s predetermined position or consciously ignoring information” (Toften and Olsen, 2004, p. 106). Symbolic use can also legitimate decisions reached on the basis of intuition or managerial assumptions (Vyas and Souchon, 2003). Although conceptual propositions of the potential relationship between each of the symbolic use dimensions and performance exist (Vyas and Souchon 2003), no empirical research has yet been undertaken. As a result, little is known about how and why symbolic use of export information may affect export performance, and under what circumstances. Furthermore, reliable and valid measures for each one of the symbolic use dimensions are absent in the literature. The purpose of this thesis is to fill in these research gaps. In so doing, a combination of both qualitative and quantitative methods is employed. The exploratory phase takes the form of in depth interviews with export decision makers in the UK. The data collected in this exploratory phase are analysed through the use of within-case and cross-case displays as per Miles and Huberman (1994) and are used not just for hypothesis development, but also to identify potential outcomes of using information symbolically in specific ways and to create pools of items for the development of measures of symbolic use. (Continues...)

Fuzzy multicriteria analysis and its applications for decision making under uncertainty

Multicriteria decision making refers to selecting or ranking alternatives from available alternatives with respect to multiple, usually conflicting criteria involving either a single decision maker or multiple decision makers. It often takes place in an environment where the information available is uncertain, subjective and imprecise. To adequately solve this decision problem, the application of fuzzy sets theory for adequately modelling the uncertainty and imprecision in multicriteria decision making has proven to be effective. Much research has been done on the development of various fuzzy multicriteria analysis approaches for effectively solving the multicriteria decision making problem, and numerous applications have been reported in the literature. In general, existing approaches can be categorized into (a) multicriteria decision making with a single decision maker and (b) multicriteria group decision making. Existing approaches, however, are not totally satisfactory due to various shortcomings that they suffer from including (a) the inability to adequately model the uncertainty and imprecision of human decision making, (b) the failure to effectively handle the requirements of decision maker(s), (c) the tedious mathematical computation required, and (d) cognitively very demanding on the decision maker(s). This research has developed four novel approaches for effectively solving the multicriteria decision making problem under uncertainty. To effectively reduce the cognitive demand on the decision maker, a pairwise comparison based approach is developed in Chapter 4 for solving the multicriteria problem under uncertainty. To adequately meet the interest of various stakeholders in the multicriteria decision making process, a decision support system (DSS) based approach is introduced in Chapter 5. In Chapter 6, a consensus oriented approach is presented in multicriteria group decision making on which a DSS is proposed for facilitating consensus building in solving the multicriteria group decision making problem. In Chapter 7, a risk-oriented approach is developed for adequately modelling the inherent risk in multicriteria group decision making with the use of the concept of ideal solutions so that the complex and unreliable process of comparing fuzzy utilities usually required in fuzzy multicriteria analysis is avoided. Empirical studies of four real fuzzy multicriteria decision making problems are presented for illustrating the applicability of the approaches developed in solving the multicriteria decision making problem. A hospital location selection problem is discussed in Chapter 8. An international distribution centre location problem is illustrated in Chapter 9. A supplier selection problem is presented in Chapter 10. A hotel location problem is discussed in Chapter 11. These studies have shown the distinct advantages of the approaches developed respectively in this research from different perspectives in solving the multicriteria decision making problem