23 research outputs found
Incremental learning algorithms and applications
International audienceIncremental learning refers to learning from streaming data, which arrive over time, with limited memory resources and, ideally, without sacrificing model accuracy. This setting fits different application scenarios where lifelong learning is relevant, e.g. due to changing environments , and it offers an elegant scheme for big data processing by means of its sequential treatment. In this contribution, we formalise the concept of incremental learning, we discuss particular challenges which arise in this setting, and we give an overview about popular approaches, its theoretical foundations, and applications which emerged in the last years
Simple but Not Simplistic: Reducing the Complexity of Machine Learning Methods
Programa Oficial de Doutoramento en Computación . 5009V01[Resumo]
A chegada do Big Data e a explosión do Internet das cousas supuxeron un gran
reto para os investigadores en Aprendizaxe Automática, facendo que o proceso de
aprendizaxe sexa mesmo roáis complexo. No mundo real, os problemas da aprendizaxe
automática xeralmente teñen complexidades inherentes, como poden ser as
caracterÃsticas intrÃnsecas dos datos, o gran número de mostras, a alta dimensión dos
datos de entrada, os cambios na distribución entre o conxunto de adestramento e
test, etc. Todos estes aspectos son importantes, e requiren novoS modelos que poi dan
facer fronte a estas situacións. Nesta tese, abordáronse todos estes problemas, tratando
de simplificar o proceso de aprendizaxe automática no escenario actual. En
primeiro lugar, realÃzase unha análise de complexidade para observar como inflúe
esta na tarefa de clasificación, e se é posible que a aplicación dun proceso previo
de selección de caracterÃsticas reduza esta complexidade. Logo, abórdase o proceso
de simplificación da fase de aprendizaxe automática mediante a filosofÃa divide e
vencerás, usando un enfoque distribuÃdo. Seguidamente, aplicamos esa mesma filosofÃa
sobre o proceso de selección de caracterÃsticas. Finalmente, optamos por un
enfoque diferente seguindo a filosofÃa do Edge Computing, a cal permite que os datos
producidos polos dispositivos do Internet das cousas se procesen máis preto de
onde se crearon. Os enfoques propostos demostraron a súa capacidade para reducir
a complexidade dos métodos de aprendizaxe automática tradicionais e, polo tanto,
espérase que a contribución desta tese abra as portas ao desenvolvemento de novos
métodos de aprendizaxe máquina máis simples, máis robustos, e máis eficientes
computacionalmente.[Resumen]
La llegada del Big Data y la explosión del Internet de las cosas han supuesto
un gran reto para los investigadores en Aprendizaje Automático, haciendo que el
proceso de aprendizaje sea incluso más complejo. En el mundo real, los problemas de
aprendizaje automático generalmente tienen complejidades inherentes) como pueden
ser las caracterÃsticas intrÃnsecas de los datos, el gran número de muestras, la alta
dimensión de los datos de entrada, los cambios en la distribución entre el conjunto de
entrenamiento y test, etc. Todos estos aspectos son importantes, y requieren nuevos
modelos que puedan hacer frente a estas situaciones. En esta tesis, se han abordado
todos estos problemas, tratando de simplificar el proceso de aprendizaje automático
en el escenario actual. En primer lugar, se realiza un análisis de complejidad para
observar cómo influye ésta en la tarea de clasificación1 y si es posible que la aplicación
de un proceso previo de selección de caracterÃsticas reduzca esta complejidad.
Luego, se aborda el proceso de simplificación de la fase de aprendizaje automático
mediante la filosofÃa divide y vencerás, usando un enfoque distribuido. A continuación,
aplicamos esa misma filosofÃa sobre el proceso de selección de caracterÃsticas.
Finalmente, optamos por un enfoque diferente siguiendo la filosofÃa del Edge Computing,
la cual permite que los datos producidos por los dispositivos del Internet de
las cosas se procesen más cerca de donde se crearon. Los enfoques propuestos han
demostrado su capacidad para reducir la complejidad de los métodos de aprendizaje
automático tnidicionales y, por lo tanto, se espera que la contribución de esta
tesis abra las puertas al desarrollo de nuevos métodos de aprendizaje máquina más
simples, más robustos, y más eficientes computacionalmente.[Abstract]
The advent of Big Data and the explosion of the Internet of Things, has brought
unprecedented challenges to Machine Learning researchers, making the learning task
more complexo Real-world machine learning problems usually have inherent complexities,
such as the intrinsic characteristics of the data, large number of instauces,
high input dimensionality, dataset shift, etc. AH these aspects matter, and can
fOI new models that can confront these situations. Thus, in this thesis, we have
addressed aH these issues) simplifying the machine learning process in the current
scenario. First, we carry out a complexity analysis to see how it inftuences the
classification models, and if it is possible that feature selection might result in a
deerease of that eomplexity. Then, we address the proeess of simplifying learning
with the divide-and-conquer philosophy of the distributed approaeh. Later, we aim
to reduce the complexity of the feature seleetion preprocessing through the same
philosophy. FinallYl we opt for a different approaeh following the eurrent philosophy
Edge eomputing, whieh allows the data produeed by Internet of Things deviees
to be proeessed closer to where they were ereated. The proposed approaehes have
demonstrated their eapability to reduce the complexity of traditional maehine learning
algorithms, and thus it is expeeted that the eontribution of this thesis will open
the doors to the development of new maehine learning methods that are simpler,
more robust, and more eomputationally efficient
Benefit maximizing classification using feature intervals
Cataloged from PDF version of article.For a long time, classification algorithms have focused on minimizing the quantity of
prediction errors by assuming that each possible error has identical consequences.
However, in many real-world situations, this assumption is not convenient. For instance,
in a medical diagnosis domain, misdiagnosing a sick patient as healthy is much more
serious than its opposite. For this reason, there is a great need for new classification
methods that can handle asymmetric cost and benefit constraints of classifications. In this
thesis, we discuss cost-sensitive classification concepts and propose a new classification
algorithm called Benefit Maximization with Feature Intervals (BMFI) that uses the
feature projection based knowledge representation. In the framework of BMFI, we
introduce five different voting methods that are shown to be effective over different
domains. A number of generalization and pruning methodologies based on benefits of
classification are implemented and experimented. Empirical evaluation of the methods
has shown that BMFI exhibits promising performance results compared to recent wrapper
cost-sensitive algorithms, despite the fact that classifier performance is highly dependent
on the benefit constraints and class distributions in the domain. In order to evaluate costsensitive
classification techniques, we describe a new metric, namely benefit accuracy
which computes the relative accuracy of the total benefit obtained with respect to the
maximum possible benefit achievable in the domain.İkizler, NazlıM.S
Determining the jet energy scale for ATLAS in the Z+Jet channel
This thesis presents a determination of the jet energy scale for the ATLAS detector using in-situ measurements. This calibration is critical, as jets are found in many analyses, and the energy measurement of jets contributes significantly to the uncertainty in numerous ATLAS results. The energy of the jet is initially taken to be the detector measurement, but this is lower than the true energy because the detector is calibrated for electromagnetic particles, not jets. One can find a correction to this energy by balancing the jet\u27s transverse momentum against a well-measured reference object. Directly calibrating the calorimeter-level jet to the particle-level is called Direct Balance; here, a different method called the Missing ET Projection Fraction (MPF) method is used instead, which balances the pt of the recoiling system against the reference object. The MPF\u27s pile-up resistant nature makes it more suitable to use in the ATLAS environment. Results for the MPF method in the Z+Jet channel are presented. A relative calibration of data to Monte Carlo simulation is provided, including a complete systematic uncertainty analysis. The uncertainty on the in-situ calibration is reduced to around 1% for most transverse momenta
MIST: a portable and efficient toolkit for molecular dynamics integration algorithm development
The main contribution of this thesis is MIST, the Molecular Integration Simula- tion Toolkit, a lightweight and efficient software library written in C++ which provides an abstract interface to common Molecular Dynamics codes, enabling rapid and portable development of new integration schemes for Molecular Dynamics. The initial release provides plug-in interfaces to NAMD-Lite, GROMACS, Amber and LAMMPS and includes several standard integration schemes, a constraint solver, temperature control using Langevin Dynamics, temperature and pressure control using Nosé-Hoover chains, and five advanced sampling schemes.
I describe the architecture, functionality and internal details of the library and the C and Fortran APIs which can be used to interface additional MD codes to MIST. As an example to future developers, each of the existing plug-ins and the integrators that are included with MIST are described. Brief instructions for compilation and use of the library are also given as a reference to users.
The library is designed to be expressive, portable and performant, and I show via a range of test systems that MIST introduces negligible overheads for serial, parallel, and GPU-accelerated cases, except for Amber where the native integrators run directly on the GPU itself, but only run on the CPU in MIST. The capabilities of MIST for production-quality simulations are demonstrated through the use of a simulated tempering simulation to study the free energy landscape of Alanine-12 in both vacuum and detailed solvent conditions.
I also present the evaluation and application of force-field and ab initio Molecular Dynamics to study the structural properties and behaviour of olivine melts. Three existing classical potentials for fayalite are tested and found to give lattice parameters and Radial Distribution Functions in good agreement with experimental data. For forsterite, lattice parameters at ambient pressure and temperature are slightly over-predicted by simulation (similar to other reported results in the literature). Likewise, higher-than expected thermal expansion coefficients and heat capacities are obtained from both ab initio and classical methods. The structure of both the crystal and melt are found to be in good agreement with experimental data. Several methodological improvements which could improve the accuracy of melting point determination and the thermal expansion coefficients are discussed
Computation in Complex Networks
Complex networks are one of the most challenging research focuses of disciplines, including physics, mathematics, biology, medicine, engineering, and computer science, among others. The interest in complex networks is increasingly growing, due to their ability to model several daily life systems, such as technology networks, the Internet, and communication, chemical, neural, social, political and financial networks. The Special Issue “Computation in Complex Networks" of Entropy offers a multidisciplinary view on how some complex systems behave, providing a collection of original and high-quality papers within the research fields of: • Community detection • Complex network modelling • Complex network analysis • Node classification • Information spreading and control • Network robustness • Social networks • Network medicin
The application of Machine Learning for Early Detection of At -Risk Learners in Massive Open Online Courses
With the rapid improvement of digital technology, Massive Open Online Courses (MOOCs) have emerged as powerful open educational learning platforms. MOOCs have been experiencing increased use and popularity in highly ranked universities in recent years. The opportunity to access high-quality courseware content within such platforms, while eliminating the burden of educational, financial and geographical obstacles has led to a growth in participant numbers. Despite the increasing participation in online courses, the low completion rate has raised major concerns in the literature. Identifying those students who are at-risk of dropping out could be a promising solution in solving the low completion rate in the online setting. Flagging at-risk students could assist the course instructors to bolster the struggling students and provide more learning resources. Although many prior studies have considered the dropout issue in the form of a sequence classification problem, such works only address a limited set of retention factors. They typically consider the learners’ activities as a sequence of weekly intervals, neglecting important learning trajectories. In this PhD thesis, my goal is to investigate retention factors. More specifically, the project seeks to explore the association of motivational trajectories, performance trajectories, engagement levels and latent engagement with the withdrawal rate. To achieve this goal, the first objective is to derive learners’ motivations based on Incentive Motivation theory. The Learning Analytic is utilised to classify student motivation into three main categories; Intrinsically motivated, Extrinsically motivated and Amotivation. Machine learning has been employed to detect the lack of motivation at early stages of the courses. The findings reveal that machine learning provides solutions that are capable of automatically identifying the students’ motivational status according to behaviourism theory. As the second and third objectives, three temporal dropout prediction models are proposed in this research work. The models provide dynamic assessment of the influence of the following factors; motivational trajectories, performance trajectories and latent engagement on students and the subsequent risk of them leaving the course. The models could assist the instructor in delivering more intensive intervention support to at-risk students. Supervised machine learning algorithms have been utilised in each model to identify the students who are in danger of dropping out in a timely manner. The results demonstrate that motivational trajectories and engagement levels are significant factors, which might influence the students’ withdrawal in online settings. On the other hand, the findings indicate that performance trajectories and latent engagement might not prevent students from completing online courses
Measurement of Detector-Corrected Cross-Sections in Events with Large Missing Transverse Momentum in Association with Jets
This thesis presents an analysis of events with large transverse missing
momentum in association with jets using 139 fb−1 of proton-proton
collisions at a centre of mass energy of 13 TeV , that was delivered at
the Large Hadron Collider and recorded using the ATLAS detector
from 2015 − 2018. The dominant process which contributes to these
events is the Z boson decaying to two neutrinos followed closely
by the contribution from W bosons decaying leptonically, in which
the charged lepton is outside the detector acceptance. The similarity
of these processes to Z and W bosons decaying leptonically can be
exploited by measuring the one lepton and two lepton regions, and
treating the leptons as invisible in order to constrain modelling along
with the experimental and theoretical uncertainties. These lepton
regions are known as the auxiliary regions.
This analysis was performed using three different phase-spaces
that are sensitive to different Dark Matter production channels. These
three phase-spaces require the ≥ 1 jet , ≥ 2 jet and VBF topologies.
The total yield is measured at the detector level and the differential
cross section is measured at the particle level as a function of the
missing transverse momentum, the dijet invariant mass and the dijet
azimuthal angle. Ratios of these cross sections are also presented
at the particle level to facilitate comparisons between regions and
minimise the systematic uncertainties.
These results are interpreted using a likelihood fit and the agree-
ment between the modelling and the data is quantified using a χ2
test and p-value. Constraints are made on the axial-vector and pseu-
doscalar simplified Dark Matter models and are shown to be competitive with results from the recent dedicated monojet-like search in ATLAS