31,240 research outputs found
Clustering techniques for human posture recognition: K-Means, FCM and SOM
An automated surveillance system should have the ability to recognize human behaviour and to warn security personnel of any impending suspicious activity. Human posture is one of the key aspects of analyzing human behaviour. We investigated three clustering techniques to recognize human posture. The system is first trained to recognize a pair of posture and this is repeated for three pairs of human posture. Finally the system is trained to recognize five postures together. The clustering techniques used for the purpose of our investigation included K-Means, fuzzy C-Means and Self-Organizing Maps. The results showed that K-Means and Fuzzy C-Means performed well for the three pair of posture data. However these clustering techniques gave low accuracy when we scale up the dataset to five different postures. Self- Organizing Maps produce better recognition accuracy when tested for five postures
How Many Dissimilarity/Kernel Self Organizing Map Variants Do We Need?
In numerous applicative contexts, data are too rich and too complex to be
represented by numerical vectors. A general approach to extend machine learning
and data mining techniques to such data is to really on a dissimilarity or on a
kernel that measures how different or similar two objects are. This approach
has been used to define several variants of the Self Organizing Map (SOM). This
paper reviews those variants in using a common set of notations in order to
outline differences and similarities between them. It discusses the advantages
and drawbacks of the variants, as well as the actual relevance of the
dissimilarity/kernel SOM for practical applications
Group Analysis of Self-organizing Maps based on Functional MRI using Restricted Frechet Means
Studies of functional MRI data are increasingly concerned with the estimation
of differences in spatio-temporal networks across groups of subjects or
experimental conditions. Unsupervised clustering and independent component
analysis (ICA) have been used to identify such spatio-temporal networks. While
these approaches have been useful for estimating these networks at the
subject-level, comparisons over groups or experimental conditions require
further methodological development. In this paper, we tackle this problem by
showing how self-organizing maps (SOMs) can be compared within a Frechean
inferential framework. Here, we summarize the mean SOM in each group as a
Frechet mean with respect to a metric on the space of SOMs. We consider the use
of different metrics, and introduce two extensions of the classical sum of
minimum distance (SMD) between two SOMs, which take into account the
spatio-temporal pattern of the fMRI data. The validity of these methods is
illustrated on synthetic data. Through these simulations, we show that the
three metrics of interest behave as expected, in the sense that the ones
capturing temporal, spatial and spatio-temporal aspects of the SOMs are more
likely to reach significance under simulated scenarios characterized by
temporal, spatial and spatio-temporal differences, respectively. In addition, a
re-analysis of a classical experiment on visually-triggered emotions
demonstrates the usefulness of this methodology. In this study, the
multivariate functional patterns typical of the subjects exposed to pleasant
and unpleasant stimuli are found to be more similar than the ones of the
subjects exposed to emotionally neutral stimuli. Taken together, these results
indicate that our proposed methods can cast new light on existing data by
adopting a global analytical perspective on functional MRI paradigms.Comment: 23 pages, 5 figures, 4 tables. Submitted to Neuroimag
Batch and median neural gas
Neural Gas (NG) constitutes a very robust clustering algorithm given
euclidian data which does not suffer from the problem of local minima like
simple vector quantization, or topological restrictions like the
self-organizing map. Based on the cost function of NG, we introduce a batch
variant of NG which shows much faster convergence and which can be interpreted
as an optimization of the cost function by the Newton method. This formulation
has the additional benefit that, based on the notion of the generalized median
in analogy to Median SOM, a variant for non-vectorial proximity data can be
introduced. We prove convergence of batch and median versions of NG, SOM, and
k-means in a unified formulation, and we investigate the behavior of the
algorithms in several experiments.Comment: In Special Issue after WSOM 05 Conference, 5-8 september, 2005, Pari
Self-Organizing Time Map: An Abstraction of Temporal Multivariate Patterns
This paper adopts and adapts Kohonen's standard Self-Organizing Map (SOM) for
exploratory temporal structure analysis. The Self-Organizing Time Map (SOTM)
implements SOM-type learning to one-dimensional arrays for individual time
units, preserves the orientation with short-term memory and arranges the arrays
in an ascending order of time. The two-dimensional representation of the SOTM
attempts thus twofold topology preservation, where the horizontal direction
preserves time topology and the vertical direction data topology. This enables
discovering the occurrence and exploring the properties of temporal structural
changes in data. For representing qualities and properties of SOTMs, we adapt
measures and visualizations from the standard SOM paradigm, as well as
introduce a measure of temporal structural changes. The functioning of the
SOTM, and its visualizations and quality and property measures, are illustrated
on artificial toy data. The usefulness of the SOTM in a real-world setting is
shown on poverty, welfare and development indicators
Fault prediction in aircraft engines using Self-Organizing Maps
Aircraft engines are designed to be used during several tens of years. Their
maintenance is a challenging and costly task, for obvious security reasons. The
goal is to ensure a proper operation of the engines, in all conditions, with a
zero probability of failure, while taking into account aging. The fact that the
same engine is sometimes used on several aircrafts has to be taken into account
too. The maintenance can be improved if an efficient procedure for the
prediction of failures is implemented. The primary source of information on the
health of the engines comes from measurement during flights. Several variables
such as the core speed, the oil pressure and quantity, the fan speed, etc. are
measured, together with environmental variables such as the outside
temperature, altitude, aircraft speed, etc. In this paper, we describe the
design of a procedure aiming at visualizing successive data measured on
aircraft engines. The data are multi-dimensional measurements on the engines,
which are projected on a self-organizing map in order to allow us to follow the
trajectories of these data over time. The trajectories consist in a succession
of points on the map, each of them corresponding to the two-dimensional
projection of the multi-dimensional vector of engine measurements. Analyzing
the trajectories aims at visualizing any deviation from a normal behavior,
making it possible to anticipate an operation failure.Comment: Communication pr\'esent\'ee au 7th International Workshop WSOM 09, St
Augustine, Floride, USA, June 200
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