Advances in Possibilistic Clustering with Application to Hyperspectral Image Processing

Η ομαδοποίηση δεδομένων είναι μια εδραιωμένη μεθοδολογία ανάλυσης δεδομένων που έχει χρησιμοποιηθεί εκτενώς σε διάφορα πεδία εφαρμογών κατά τη διάρκεια των τελευταίων δεκαετιών. Η παρούσα διατριβή εστιάζει κυρίως στην ευρύτερη οικογένεια των αλγορίθμων βελτιστοποίησης κόστους και πιο συγκεκριμένα στους αλγόριθμους ομαδοποίησης με βάση τα ενδεχόμενα (Possibilistic c-Means, PCM). Συγκεκριμένα, αφού εκτίθενται τα αδύνατα σημεία τους, προτείνονται νέοι (batch και online) PCM αλγόριθμοι που αποτελούν επεκτάσεις των προηγουμένων και αντιμετωπίζουν τα αδύνατα σημεία των πρώτων. Οι προτεινόμενοι αλγόριθμοι ομαδοποίησης βασίζονται κυρίως στην υιοθέτηση των εννοιών (α) της προσαρμοστικότητας παραμέτρων (parameter adaptivity), οι οποίες στους κλασσικούς PCM αλγορίθμους παραμένουν σταθερές κατά την εκτέλεσή τους και (β) της αραιότητας (sparsity). Αυτά τα χαρακτηριστικά προσδίδουν νέα δυναμική στους προτεινόμενους αλγορίθμους οι οποίοι πλέον: (α) είναι (κατ' αρχήν) σε θέση να προσδιορίσουν τον πραγματικό αριθμό των φυσικών ομάδων που σχηματίζονται από τα δεδομένα, (β) είναι ικανοί να αποκαλύψουν την υποκείμενη δομή ομαδοποίησης, ακόμη και σε δύσκολες περιπτώσεις, όπου οι φυσικές ομάδες βρίσκονται κοντά η μία στην άλλη ή/και έχουν σημαντικές διαφορές στις διακυμάνσεις ή/και στις πυκνότητές τους και (γ) είναι εύρωστοι στην παρουσία θορύβου και ακραίων σημείων. Επίσης, δίνονται θεωρητικά αποτελέσματα σχετικά με τη σύγκλιση των προτεινόμενων αλγορίθμων, τα οποία βρίσκουν επίσης εφαρμογή και στους κλασσικούς PCM αλγορίθμους. Η δυναμική των προτεινόμενων αλγορίθμων αναδεικνύεται μέσω εκτεταμένων πειραμάτων, τόσο σε συνθετικά όσο και σε πραγματικά δεδομένα. Επιπλέον, οι αλγόριθμοι αυτοί έχουν εφαρμοστεί με επιτυχία στο ιδιαίτερα απαιτητικό πρόβλημα της ομαδοποίησης σε υπερφασματικές εικόνες. Τέλος, αναπτύχθηκε και μια μέθοδος επιλογής χαρακτηριστικών κατάλληλη για υπερφασματικές εικόνες.Clustering is a well established data analysis methodology that has been extensively used in various fields of applications during the last decades. The main focus of the present thesis is on a well-known cost-function optimization-based family of clustering algorithms, called Possibilistic C-Means (PCM) algorithms. Specifically, the shortcomings of PCM algorithms are exposed and novel batch and online PCM schemes are proposed to cope with them. These schemes rely on (i) the adaptation of certain parameters which remain fixed during the execution of the original PCMs and (ii) the adoption of sparsity. The incorporation of these two characteristics renders the proposed schemes: (a) capable, in principle, to reveal the true number of physical clusters formed by the data, (b) capable to uncover the underlying clustering structure even in demanding cases, where the physical clusters are closely located to each other and/or have significant differences in their variances and/or densities, and (c) immune to the presence of noise and outliers. Moreover, theoretical results concerning the convergence of the proposed algorithms, also applicable to the classical PCMs, are provided. The potential of the proposed methods is demonstrated via extensive experimentation on both synthetic and real data sets. In addition, they have been successfully applied on the challenging problem of clustering in HyperSpectral Images (HSIs). Finally, a feature selection technique suitable for HSIs has also been developed

RecPOID: POI Recommendation with Friendship Aware and Deep CNN

In location-based social networks (LBSNs), exploit several key features of points-of-interest (POIs) and users on precise POI recommendation be significant. In this work, a novel POI recommenda-tion pipeline based on the convolutional neural network named RecPOID is proposed, which can recommend an accurate sequence of top-k POIs and considers only the effect of the most similar pattern friendship rather than all user’s friendship. We use the fuzzy c-mean clustering method to find the similarity. Temporal and spatial features of similar friends are fed to our Deep CNN model. The 10-layer convolutional neural network can predict longitude and latitude and the Id of the next proper locations; after that, based on the shortest time distance from a similar pattern’s friendship, select the smallest distance locations. The proposed structure uses six features, includ-ing user’s ID, month, day, hour, minute, and second of visiting time by each user as inputs. RecPOID based on two accessible LBSNs datasets is evaluated. Experimental outcomes illustrate considering most similar friendship could improve the accuracy of recommendations and the proposed RecPOID for POI recommendation outperforms state-of-the-art approaches

An extended Takagi–Sugeno–Kang inference system (TSK+) with fuzzy interpolation and its rule base generation

A rule base covering the entire input domain is required for the conventional Mamdani inference and Takagi-Sugeno-Kang (TSK) inference. Fuzzy interpolation enhances conventional fuzzy rule inference systems by allowing the use of sparse rule bases by which certain inputs are not covered. Given that almost all of the existing fuzzy interpolation approaches were developed to support the Mamdani inference, this paper presents a novel fuzzy interpolation approach that extends the TSK inference. This paper also proposes a data-driven rule base generation method to support the extended TSK inference system. The proposed system enhances the conventional TSK inference in two ways: 1) workable with incomplete or unevenly distributed data sets or incomplete expert knowledge that entails only a sparse rule base, and 2) simplifying complex fuzzy inference systems by using more compact rule bases for complex systems without the sacrificing of system performance. The experimentation shows that the proposed system overall outperforms the existing approaches with the utilisation of smaller rule bases

Machine learning in solar physics

The application of machine learning in solar physics has the potential to greatly enhance our understanding of the complex processes that take place in the atmosphere of the Sun. By using techniques such as deep learning, we are now in the position to analyze large amounts of data from solar observations and identify patterns and trends that may not have been apparent using traditional methods. This can help us improve our understanding of explosive events like solar flares, which can have a strong effect on the Earth environment. Predicting hazardous events on Earth becomes crucial for our technological society. Machine learning can also improve our understanding of the inner workings of the sun itself by allowing us to go deeper into the data and to propose more complex models to explain them. Additionally, the use of machine learning can help to automate the analysis of solar data, reducing the need for manual labor and increasing the efficiency of research in this field.Comment: 100 pages, 13 figures, 286 references, accepted for publication as a Living Review in Solar Physics (LRSP