Persona:
Fernández Galán, Severino

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0000-0003-3767-7480
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Fernández Galán
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Severino
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20192
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Fecha de finalización: 2019 ×

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Mostrando 1 - 2 de 2
  • Miniatura
    Publicación
    Comparative Evaluation of Region Query Strategies for DBSCAN Clustering
    (Elsevier, 2019-10) Fernández Galán, Severino
    Clustering is a technique that allows data to be organized into groups of similar objects. DBSCAN (Density-Based Spatial Clustering of Applications with Noise) constitutes a popular clustering algorithm that relies on a density-based notion of cluster and is designed to discover clusters of arbitrary shape. The computational complexity of DBSCAN is dominated by the calculation of the ϵ-neighborhood for every object in the dataset. Thus, the efficiency of DBSCAN can be improved in two different ways: (1) by reducing the overall number of ϵ-neighborhood queries (also known as region queries), or (2) by reducing the complexity of the nearest neighbor search conducted for each region query. This paper deals with the first issue by considering the most relevant region query strategies for DBSCAN, all of them characterized by inspecting the neighborhoods of only a subset of the objects in the dataset. We comparatively evaluate these region query strategies (or DBSCAN variants) in terms of clustering effectiveness and efficiency; additionally, a novel region query strategy is introduced in this work. The results show that some specific DBSCAN variants are only slightly inferior to DBSCAN in terms of effectiveness, while greatly improving its efficiency. Among these variants, the novel one outperforms the rest.
  • Miniatura
    Publicación
    Fast Evacuation Method: using an effective dynamic floor field based on efficient pedestrian assignment
    (Elsevier, 2019-12) Fernández Galán, Severino
    The problem of pedestrian evacuation can be addressed through cellular automata incorporating a floor field that indicates promising movements to pedestrians. The two main types of floor field are the static, which represents the shortest path from each cell to an exit (and is usually combined with dynamic measures such as the density or distribution of pedestrians), and the dynamic, which represents the quickest path from each cell to an exit. The second type has been widely used recently, since it gives rise to more efficient and realistic simulations of pedestrian dynamics. The goal of these two types of floor field is to minimize the travel time for each pedestrian; however, this paper tackles the evacuation problem from a different perspective: The time taken by the whole evacuation process is optimized. For that purpose, a floor field is constructed by assigning pedestrians to exits such that the estimated time for complete evacuation is minimized. An experimental evaluation is conducted to compare the new fast evacuation method with competitive methods using floor fields based on quickest paths: Flood Fill and the Fast Marching Method. The results show that the new method is effective in terms of the number of time steps for complete evacuation and efficient regarding the total simulation runtime.