2017
Delgado, Maria Soledad; Higuera, Clara; Calle-Espinosa, Jorge; Morán, Federico; Montero, Francisco
A SOM prototype-based cluster analysis methodology Journal Article
In: Expert Systems with Applications, vol. 88, pp. 14-28, 2017, ISSN: 0957-4174.
Abstract | Links | BibTeX | Tags: Clustering, Metabolic network, Self-organizing map, Topology preserving, Unsupervised
@article{DELGADO201714,
title = {A SOM prototype-based cluster analysis methodology},
author = {Maria Soledad Delgado and Clara Higuera and Jorge Calle-Espinosa and Federico Morán and Francisco Montero},
url = {https://www.sciencedirect.com/science/article/pii/S0957417417304396},
doi = {https://doi.org/10.1016/j.eswa.2017.06.022},
issn = {0957-4174},
year = {2017},
date = {2017-01-01},
journal = {Expert Systems with Applications},
volume = {88},
pages = {14-28},
abstract = {Data clustering is aimed at finding groups of data that share common hidden properties. These kinds of techniques are especially critical at early stages of data analysis where no information about the dataset is available. One of the mayor shortcomings of the clustering algorithms is the difficulty for non-experts users to configure them and, in some cases, interpret the results. In this work a computational approach with a two-layer structure based on Self-Organizing Map (SOM) is presented for cluster analysis. In the first level, a quantization of the data samples using topology-preserving metrics to automatically determine the number of units in the SOM is proposed. In the second level the obtained SOM prototypes are clustered by means of a connectivity analysis to explore the quality of the partitioning with different number of clusters. The most important benefit of this two-layer procedure is that computational load decreases considerably in comparison with data based clustering methods, making it possible to cluster large data sets and to consider several different clustering alternatives in a limited time. This methodology produces a two-dimensional map representation of the, usually, high dimensional input space, along with quantitative information on viable clustering alternatives, which facilitates the exploration of the possible partitions in a dataset. The efficiency and interpretation of the methodology is illustrated by its application to artificial, benchmark and real complex biological datasets. The experimental results demonstrate the ability of the method to identify possible segmentations in a dataset, compared to algorithms that only yield a single clustering solution. The proposed algorithm tackles the intrinsic limitations of SOM and the parameter settings associated with the clustering methodology, without requiring the number of clusters or the SOM architecture as a prerequisite, among others. This way, it makes possible its application even by researchers with a limited expertise in machine learning.},
keywords = {Clustering, Metabolic network, Self-organizing map, Topology preserving, Unsupervised},
pubstate = {published},
tppubtype = {article}
}
Data clustering is aimed at finding groups of data that share common hidden properties. These kinds of techniques are especially critical at early stages of data analysis where no information about the dataset is available. One of the mayor shortcomings of the clustering algorithms is the difficulty for non-experts users to configure them and, in some cases, interpret the results. In this work a computational approach with a two-layer structure based on Self-Organizing Map (SOM) is presented for cluster analysis. In the first level, a quantization of the data samples using topology-preserving metrics to automatically determine the number of units in the SOM is proposed. In the second level the obtained SOM prototypes are clustered by means of a connectivity analysis to explore the quality of the partitioning with different number of clusters. The most important benefit of this two-layer procedure is that computational load decreases considerably in comparison with data based clustering methods, making it possible to cluster large data sets and to consider several different clustering alternatives in a limited time. This methodology produces a two-dimensional map representation of the, usually, high dimensional input space, along with quantitative information on viable clustering alternatives, which facilitates the exploration of the possible partitions in a dataset. The efficiency and interpretation of the methodology is illustrated by its application to artificial, benchmark and real complex biological datasets. The experimental results demonstrate the ability of the method to identify possible segmentations in a dataset, compared to algorithms that only yield a single clustering solution. The proposed algorithm tackles the intrinsic limitations of SOM and the parameter settings associated with the clustering methodology, without requiring the number of clusters or the SOM architecture as a prerequisite, among others. This way, it makes possible its application even by researchers with a limited expertise in machine learning.
2011
Delgado, Maria Soledad; Gonzalo, Consuelo; Martinez, Estibaliz; Arquero, Agueda
A combined measure for quantifying and qualifying the topology preservation of growing self-organizing maps Journal Article
In: Neurocomputing, vol. 74, no. 16, pp. 2624-2632, 2011, ISSN: 0925-2312, (Advances in Extreme Learning Machine: Theory and Applications Biological Inspired Systems. Computational and Ambient Intelligence).
Abstract | Links | BibTeX | Tags: Delaunay triangulation, Growing cell structures, Self-organizing map, Topology preserving, Visualization methods
@article{DELGADO20112624,
title = {A combined measure for quantifying and qualifying the topology preservation of growing self-organizing maps},
author = {Maria Soledad Delgado and Consuelo Gonzalo and Estibaliz Martinez and Agueda Arquero},
url = {https://www.sciencedirect.com/science/article/pii/S0925231211002396},
doi = {https://doi.org/10.1016/j.neucom.2011.03.021},
issn = {0925-2312},
year = {2011},
date = {2011-01-01},
journal = {Neurocomputing},
volume = {74},
number = {16},
pages = {2624-2632},
abstract = {The Self-Organizing Map (SOM) is a neural network model that performs an ordered projection of a high dimensional input space in a low-dimensional topological structure. The process in which such mapping is formed is defined by the SOM algorithm, which is a competitive, unsupervised and nonparametric method, since it does not make any assumption about the input data distribution. The feature maps provided by this algorithm have been successfully applied for vector quantization, clustering and high dimensional data visualization processes. However, the initialization of the network topology and the selection of the SOM training parameters are two difficult tasks caused by the unknown distribution of the input signals. A misconfiguration of these parameters can generate a feature map of low-quality, so it is necessary to have some measure of the degree of adaptation of the SOM network to the input data model. The topology preservation is the most common concept used to implement this measure. Several qualitative and quantitative methods have been proposed for measuring the degree of SOM topology preservation, particularly using Kohonen's model. In this work, two methods for measuring the topology preservation of the Growing Cell Structures (GCSs) model are proposed: the topographic function and the topology preserving map.},
note = {Advances in Extreme Learning Machine: Theory and Applications Biological Inspired Systems. Computational and Ambient Intelligence},
keywords = {Delaunay triangulation, Growing cell structures, Self-organizing map, Topology preserving, Visualization methods},
pubstate = {published},
tppubtype = {article}
}
The Self-Organizing Map (SOM) is a neural network model that performs an ordered projection of a high dimensional input space in a low-dimensional topological structure. The process in which such mapping is formed is defined by the SOM algorithm, which is a competitive, unsupervised and nonparametric method, since it does not make any assumption about the input data distribution. The feature maps provided by this algorithm have been successfully applied for vector quantization, clustering and high dimensional data visualization processes. However, the initialization of the network topology and the selection of the SOM training parameters are two difficult tasks caused by the unknown distribution of the input signals. A misconfiguration of these parameters can generate a feature map of low-quality, so it is necessary to have some measure of the degree of adaptation of the SOM network to the input data model. The topology preservation is the most common concept used to implement this measure. Several qualitative and quantitative methods have been proposed for measuring the degree of SOM topology preservation, particularly using Kohonen's model. In this work, two methods for measuring the topology preservation of the Growing Cell Structures (GCSs) model are proposed: the topographic function and the topology preserving map.