Browsing by Author "Demirhan, Melek"

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    A Fuzzy Areal Assessment Approach for Potentially Contaminated Sites
    (PERGAMON-ELSEVIER SCIENCE LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND, 2000-04) Özdamar, Linet; Demirhan, Melek; Özpınar, Alper; KILANÇ, BURAK
    This article describes a new fuzzy areal site assessment approach in the detection of contaminated zones within a site which is under environmental investigation. Conventional techniques utilized in this held are mostly interpolation based. These methods interpolate the contaminant concentration values at unobserved locations using observed values. Unlike these interpolation techniques, the motivation of the approach introduced here consists of partitioning a given site into smaller sections. Partitioning is carried out iteratively where subregions of interest are divided into further smaller regions. This re-partitioning scheme leads to a dynamic grouping of observations, since areas of differing sizes and boundaries contain different sets of samples. The potential of an area to contain contaminated zones is assessed by a fuzzy measure which converts the data values in that area into an aggregate grade normalized on [0, 1]. Thus, this approach does not assume concentration values at unobserved locations, rather, an areal potential is evaluated.
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    A Note On the Use of a Fuzzy Approach in Adaptive Partitioning Algorithms for Global Optimization
    (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 445 HOES LANE, PISCATAWAY, NJ 08855-4141 USA, 1999-08) Demirhan, Melek; Özdamar, Linet
    In global optimization, adaptive partitioning algorithms (APA) operate on the basis of partitioning the feasible region into subregions, sampling and evaluating each subregion, and selecting one or more subregions for repartitioning, The purpose of the repartitioning process is to locate a narrow neighborhood around the global optimum. In this correspondence, He propose to use a fuzzy approach in the assessment of subregions using random samples taken from these subregions. We discuss different types of uncertainties involved in APA and ne conclude that the use of a fuzzy approach in the assessment of subregions is in concurrence with APA's convergence property, We provide numerical results for the fuzzy approach on 13 test functions from the literature.
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    Experiments with New Stochastic Global Optimization Search Techniques
    (PERGAMON-ELSEVIER SCIENCE LTD., 2000-08) ÖZDAMAR, LİNET; Demirhan, Melek
    In this paper several probabilistic search techniques are developed for global optimization under three heuristic classifications: simulated annealing, clustering methods and adaptive partitioning algorithms. The algorithms proposed here combine different methods found in the literature and they are compared with well-established approaches in the corresponding areas. Computational results are obtained on 77 small to moderate size (up to 10 variables) nonlinear test functions with simple bounds and Is large size test functions (up to 400 variables) collected from literature.