DME - Artigos em Revistas Internacionais / Articles in International Journals
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- Multi-outlet retail site location assessment : a state of the artPublication . Mendes, Armando B.; Themido, Isabel H.One of the most important decisions a retailer can make is where to locate a retail outlet. Because convenience is so important to today's consumers, a retail store can prosper or fail solely based on its location. Recently, a changing retail environment is augmenting the location importance as retail economic groups develop multi-outlet chains of small stores. The methods used in the development and calibration of location models for commercial spaces and sales forecast are multiple, varying from simple analogy forecast models to very complex spatial interactions models, which may incorporate dependence models in a gravitational or logit structure and many exploratory variables. More recent developments incorporating meta-heuristics such as genetic algorithms for the global problem of the multi-outlet chain configuration, or the use of Voronoi diagrams in store trade area delimitation, are also presented. Finally, the Geographical Information Systems' role on the decision support process is equally explored.
- A new approach to factorization of a class of almost-periodic triangular symbols and related Riemann-Hilbert problems.Publication . Câmara, Maria Cristina; Santos, António Ferreira dos; Martins, Maria do CarmoThe factorization of almost-periodic triangular symbols, G, associated to finite-interval convolution operators is studied for two classes of operators whose Fourier symbols are almost periodic polynomials with spectrum in the group αZ+βZ+ZαZ+βZ+Z (α,β∈]0,1[α,β∈]0,1[, α+β>1α+β>1, α/β∉Qα/β∉Q). The factorization problem is solved by a method that is based on the calculation of one solution of the Riemann-Hilbert problem GΦ+=Φ−GΦ+=Φ− in L∞(R)L∞(R) and does not require solving the associated corona problems since a second linearly independent solution is obtained by means of an appropriate transformation on the space of solutions to the Riemann-Hilbert problem. Some unexpected, but interesting, results are obtained concerning the Fourier spectrum of the solutions of GΦ+=Φ−GΦ+=Φ−. In particular it is shown that a solution exists with Fourier spectrum in the additive group αZ+βZαZ+βZ whether this group contains ZZ or not. Possible application of the method to more general classes of symbols is considered in the last section of the paper.
- Clustering supermarkets: the role of expertsPublication . Mendes, Armando B.; Cardoso, Margarida G.M.S.This work is part of a supermarket chain expansion study and is intended to cluster the existent outlets in order to support the evaluation of outlet performance and new outlet site location. To overcome the curse of dimensionality (a large number of attributes for a very small number of existing outlets) experts' knowledge is considered in the clustering process. Three alternative approaches are compared for this end, the experts being required to: (1) a priori: provide values for perceived dissimilarities between pairs of outlets; (2) a posteriori: evaluate results from alternative regression trees; (3) interactively: help to select base variables and evaluate results from alternative dendrograms. The later approach provided the best results according to the marketing experts.
- Explicit almost-periodic factorization for a class of triangular matrix functionsPublication . Câmara, Maria Cristina; Martins, Maria do CarmoThe canonical generalized factorization of a class of 2×2 triangular matrix symbols associated to convolution operators on a finite interval is studied. A case is considered in which the non-diagonal entry is an almost-periodic trinomial whose spectrum consists of the point zero and two other points of different signs whose distance is less than 1. Explicit formulas for the factors of such a factorization are obtained.
- Flat portions on the boundary of the indefinite numerical range of 3×3 matricesPublication . Teixeira, Ricardo Emanuel Cunha; Bebiano, Natália; Providência, João daWe focus on complex 3×3 matrices whose indefinite numerical ranges have a flat portion on the boundary. The results here obtained are parallel to those of Keeler, Rodman and Spitkovsky for the classical numerical range.
- An Approach to Variable Aggregation in Efficiency AnalysisPublication . Noncheva, Veska; Mendes, Armando B.; Silva, EmilianaIn the nonparametric framework of Data Envelopment Analysis the statistical properties of its estimators have been investigated and only asymptotic results are available. For DEA estimators results of practical use have been proved only for the case of one input and one output. However, in the real world problems the production process is usually well described by many variables. In this paper a machine learning approach to variable aggregation based on Canonical Correlation Analysis is presented. This approach is applied for efficiency estimation of all the farms in Terceira Island of the Azorean archipelago.
- Measuring similarity of complex and heterogeneous data in clustering of large data setsPublication . Bacelar-Nicolau, Helena; Nicolau, Fernando C.; Sousa, Áurea; Bacelar-Nicolau, LeonorCluster analysis or classification usually concerns a set of exploratory multivariate data analysis methods and techniques for finding a clustering structure on a dataset. That may refer either to groups of statistical data units or to groups of variables. In this work we deal with a generalization of this paradigm concerning clustering of complex data described by three different types of variables, frequently present in a three-way context. We obtain compatible versions of the same affinity coefficient for measuring similarity between statistical data units described by those three types of variables. A global generalized similarity coefficient is analyzed for such kind of mixed data, often arising in data mining or knowledge mining.
- Indefinite numerical range of 3×3 matricesPublication . Teixeira, Ricardo Emanuel Cunha; Bebiano, Natália; Providência, João daThe point equation of the associated curve of the indefinite numerical range is derived, following Fiedler’s approach for definite inner product spaces. The classification of the associated curve is presented in the 3 × 3 indefinite case, using Newton’s classification of cubic curves. Illustrative examples of all the different possibilities are given. The results obtained extend to Krein spaces results of Kippenhahn on the classical numerical range.
- Weighted Generalised Affinity Coefficient in Cluster Analysis of Complex Data of the Interval TypePublication . Sousa, Áurea; Nicolau, Fernando C.; Bacelar-Nicolau, Helena; Silva, OsvaldoComplex Data Analysis is a relatively new field that provides a range of methods for analyzing complex/symbolic data, and can be defined as the extension of standard data analysis to more complex data tables. There are two steps in Complex or Symbolic Data Analysis: i) knowledge extraction from large databases as in Data Mining; and ii) application of new tools to the extracted knowledge in order to extend Data Mining to Knowledge Mining. The weighted generalized affinity coefficient appears to be an appropriate resemblance measure between elements (statistical data units or variables) in cases where we deal with complex data from large databases. In this work we apply two different processes to determine values of the weighted generalized affinity coefficient in the case where we are dealing with data units described by variables whose values are intervals of the real axis. We present one example concerned with real data (with a known structure) in the field of Biometry, in which objects are described by variables whose values are intervals, in order to illustrate the effectiveness of Ascendant Hierarchical Cluster Analysis based on the weighted generalized affinity coefficient and classical and/or probabilistic aggregation criteria. In this example, we applied a method of validation to identify the best partitions.
- Prorural: Program assessment in an involved actor's perspectivePublication . Silva, Emiliana; Mendes, Armando B.PRORURAL- Azores Rural Development Plan - for 2007 to 2013, is the European Union rural development policy adjusted to the Azores Region and it is supported by European Agricultural Fund for Rural Development. The PRORURAL was approved by Commission Decision C (2007) 6162, on the 4th of December 2007. The PRORURAL has four center lines: 1) improving competitiveness of the agricultural and forestry sectors; 2) improvement of the environment and rural landscape; 3) quality of life in rural areas and diversification of economy; and 4) operation of LAGs, Acquisition of skills and entertainment in rural areas. The financial implementation rate was 34% and its approval rate was about 60% as regards to plan´s total allocation. This higher performance achieved in the material and financial execution was the result of the concerted effort between all entities in charges of the programmer’s management and the commitment and initiative of the beneficiaries despite the economic crises period. The objective of this research is the assessment of the PRORURAL in an engaged actor’s perspective. For that, it was established an expert panel, constituted mainly by farmers. A questionnaire was made and a Strengths, Weaknesses/Limitations, Opportunities, and Threats –SWOT- matrix is presented.