Dissertations / Theses on the topic 'Riemannian and barycentric geometry'
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Farina, Sofia. "Barycentric Subspace Analysis on the Sphere and Image Manifolds." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/15797/.
Full textLord, Steven. "Riemannian non-commutative geometry /." Title page, abstract and table of contents only, 2002. http://web4.library.adelaide.edu.au/theses/09PH/09phl8661.pdf.
Full textMaignant, Elodie. "Plongements barycentriques pour l'apprentissage géométrique de variétés : application aux formes et graphes." Electronic Thesis or Diss., Université Côte d'Azur, 2023. http://www.theses.fr/2023COAZ4096.
Full textAn MRI image has over 60,000 pixels. The largest known human protein consists of around 30,000 amino acids. We call such data high-dimensional. In practice, most high-dimensional data is high-dimensional only artificially. For example, of all the images that could be randomly generated by coloring 256 x 256 pixels, only a very small subset would resemble an MRI image of a human brain. This is known as the intrinsic dimension of such data. Therefore, learning high-dimensional data is often synonymous with dimensionality reduction. There are numerous methods for reducing the dimension of a dataset, the most recent of which can be classified according to two approaches.A first approach known as manifold learning or non-linear dimensionality reduction is based on the observation that some of the physical laws behind the data we observe are non-linear. In this case, trying to explain the intrinsic dimension of a dataset with a linear model is sometimes unrealistic. Instead, manifold learning methods assume a locally linear model.Moreover, with the emergence of statistical shape analysis, there has been a growing awareness that many types of data are naturally invariant to certain symmetries (rotations, reparametrizations, permutations...). Such properties are directly mirrored in the intrinsic dimension of such data. These invariances cannot be faithfully transcribed by Euclidean geometry. There is therefore a growing interest in modeling such data using finer structures such as Riemannian manifolds. A second recent approach to dimension reduction consists then in generalizing existing methods to non-Euclidean data. This is known as geometric learning.In order to combine both geometric learning and manifold learning, we investigated the method called locally linear embedding, which has the specificity of being based on the notion of barycenter, a notion a priori defined in Euclidean spaces but which generalizes to Riemannian manifolds. In fact, the method called barycentric subspace analysis, which is one of those generalizing principal component analysis to Riemannian manifolds, is based on this notion as well. Here we rephrase both methods under the new notion of barycentric embeddings. Essentially, barycentric embeddings inherit the structure of most linear and non-linear dimension reduction methods, but rely on a (locally) barycentric -- affine -- model rather than a linear one.The core of our work lies in the analysis of these methods, both on a theoretical and practical level. In particular, we address the application of barycentric embeddings to two important examples in geometric learning: shapes and graphs. In addition to practical implementation issues, each of these examples raises its own theoretical questions, mostly related to the geometry of quotient spaces. In particular, we highlight that compared to standard dimension reduction methods in graph analysis, barycentric embeddings stand out for their better interpretability. In parallel with these examples, we characterize the geometry of locally barycentric embeddings, which generalize the projection computed by locally linear embedding. Finally, algorithms for geometric manifold learning, novel in their approach, complete this work
Lidberg, Petter. "Barycentric and harmonic coordinates." Thesis, Uppsala universitet, Algebra och geometri, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-179487.
Full textHall, Stuart James. "Numerical methods and Riemannian geometry." Thesis, Imperial College London, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.538692.
Full textFerreira, Ana Cristina Castro. "Riemannian geometry with skew torsion." Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526550.
Full textWu, Bao Qiang. "Geometry of complete Riemannian Submanifolds." Lyon 1, 1998. http://www.theses.fr/1998LYO10064.
Full textBoarotto, Francesco. "Topics in sub-Riemannian geometry." Doctoral thesis, SISSA, 2016. http://hdl.handle.net/20.500.11767/4881.
Full textPalmer, Ian Christian. "Riemannian geometry of compact metric spaces." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34744.
Full textRaineri, Emanuele. "Quantum Riemannian geometry of finite sets." Thesis, Queen Mary, University of London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414738.
Full textHabermann, Karen. "Geometry of sub-Riemannian diffusion processes." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/271855.
Full textDunn, Corey. "Curvature homogeneous pseudo-Riemannian manifolds /." view abstract or download file of text, 2006. http://proquest.umi.com/pqdweb?did=1188874491&sid=3&Fmt=2&clientId=11238&RQT=309&VName=PQD.
Full textTypescript. Includes vita and abstract. Includes bibliographical references (leaves 146-147). Also available for download via the World Wide Web; free to University of Oregon users.
Lärz, Kordian. "Global aspects of holonomy in pseudo-Riemannian geometry." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät II, 2011. http://dx.doi.org/10.18452/16363.
Full textIn this thesis we study the interaction of holonomy and the global geometry of Lorentzian manifolds and pseudo-Riemannian submanifolds in spaces of constant curvature. In particular, we construct weakly irreducible, reducible Lorentzian metrics on the total spaces of certain circle bundles leading to a construction of Lorentzian manifolds with specified holonomy representations. Then we introduce a Bochner technique for Lorentzian manifolds admitting a nowhere vanishing parallel lightlike vector field whose orthogonal distribution has compact leaves. Finally, we classify normal holonomy representations of spacelike submanifolds in spaces of constant curvature and extend the classification to more general submanifolds.
Schiappa, Ricardo. "Aspects of Riemannian geometry in quantum field theories." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/85337.
Full textGhezzi, Roberta. "Almost-Riemannian Geometry from a Control Theoretical Viewpoint." Doctoral thesis, SISSA, 2010. http://hdl.handle.net/20.500.11767/4140.
Full textCollin, Jan-Ola. "The Existence of Riemannian Metrics on Real Vector Bundles." Thesis, Umeå universitet, Institutionen för matematik och matematisk statistik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-151964.
Full textI denna uppsats presenterar vi ett självständigt bevis på existensen av Riemannskametriker på reella vektorbuntar.
Becker, Christian. "On the Riemannian geometry of Seiberg-Witten moduli spaces." Phd thesis, [S.l. : s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=975744771.
Full textMajid, Shahn, and Andreas Cap@esi ac at. "Riemannian Geometry of Quantum Groups and Finite Groups with." ESI preprints, 2000. ftp://ftp.esi.ac.at/pub/Preprints/esi902.ps.
Full textPaulat, Martin [Verfasser]. "Sub-Riemannian geometry and heat kernel estimates / Martin Paulat." Kiel : Universitätsbibliothek Kiel, 2008. http://d-nb.info/1019659203/34.
Full textBullo, Francesco Murray Richard M. "Nonlinear control of mechanical systems : a Riemannian geometry approach /." Diss., Pasadena, Calif. : California Institute of Technology, 1999. http://resolver.caltech.edu/CaltechETD:etd-02072008-100242.
Full textNicolussi, Golo Sebastiano. "Topics in the geometry of non Riemannian lie groups." Doctoral thesis, Università degli studi di Trento, 2017. https://hdl.handle.net/11572/367715.
Full textNicolussi, Golo Sebastiano. "Topics in the geometry of non Riemannian lie groups." Doctoral thesis, University of Trento, 2017. http://eprints-phd.biblio.unitn.it/2668/1/SebastianoNicolussiGolo-PhDThesisUnitn.pdf.
Full textBarilari, Davide. "Invariants, volumes and heat kernels in sub-Riemannian geometry." Doctoral thesis, SISSA, 2011. http://hdl.handle.net/20.500.11767/4631.
Full textGentile, Alessandro. "Geodesics and horizontal-path spaces in sub-Riemannian geometry." Doctoral thesis, SISSA, 2014. http://hdl.handle.net/20.500.11767/3901.
Full textLi, Chengbo. "Parametrized Curves in Lagrange Grassmannians and Sub-Riemannian Geometry." Doctoral thesis, SISSA, 2009. http://hdl.handle.net/20.500.11767/4625.
Full textFrost, George. "The projective parabolic geometry of Riemannian, Kähler and quaternion-Kähler metrics." Thesis, University of Bath, 2016. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.690742.
Full textWells, Matthew J. "ASPECTS OF THE GEOMETRY OF METRICAL CONNECTIONS." UKnowledge, 2009. http://uknowledge.uky.edu/gradschool_diss/749.
Full textLaGatta, Tom. "Geodesics of Random Riemannian Metrics." Diss., The University of Arizona, 2010. http://hdl.handle.net/10150/193749.
Full textStavrov, Iva. "Spectral geometry of the Riemann curvature tensor /." view abstract or download file of text, 2003. http://wwwlib.umi.com/cr/uoregon/fullcit?p3095275.
Full textTypescript. Includes vita and abstract. Includes bibliographical references (leaves 236-241). Also available for download via the World Wide Web; free to University of Oregon users.
Alekseevsky, Dmitri, Andreas Kriegl, Mark Losik, Peter W. Michor, and Peter Michor@esi ac at. "The Riemannian Geometry of Orbit Spaces. The Metric, Geodesics, and." ESI preprints, 2001. ftp://ftp.esi.ac.at/pub/Preprints/esi997.ps.
Full textElsabrouty, Maha. "Riemannian geometry based blind signal separation using independent component analysis." Thesis, University of Ottawa (Canada), 2006. http://hdl.handle.net/10393/29291.
Full textMalchiodi, Andrea. "Existence and multiplicity results for some problems in Riemannian geometry." Doctoral thesis, SISSA, 2000. http://hdl.handle.net/20.500.11767/4627.
Full textOnodera, Mitsuko. "Study of rigidity problems for C2[pi]-manifolds." Sendai : Tohoku Univ, 2006. http://www.gbv.de/dms/goettingen/52860726X.pdf.
Full textRizzi, Luca. "The curvature of optimal control problems with applications to sub-Riemannian geometry." Doctoral thesis, SISSA, 2014. http://hdl.handle.net/20.500.11767/4841.
Full textPearson, John Clifford. "The noncommutative geometry of ultrametric cantor sets." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24657.
Full textCommittee Chair: Bellissard, Jean; Committee Member: Baker, Matt; Committee Member: Bakhtin, Yuri; Committee Member: Garoufalidis, Stavros; Committee Member: Putnam, Ian
StClair, Jessica Lindsey. "Geometry of Spaces of Planar Quadrilaterals." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/26887.
Full textPh. D.
Persson, Nicklas. "Shortest paths and geodesics in metric spaces." Thesis, Umeå universitet, Institutionen för matematik och matematisk statistik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-66732.
Full textFeppon, Florian (Florian Jeremy). "Riemannian geometry of matrix manifolds for Lagrangian uncertainty quantification of stochastic fluid flows." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111041.
Full textCataloged from PDF version of thesis.
Includes bibliographical references (pages 119-129).
This work focuses on developing theory and methodologies for the analysis of material transport in stochastic fluid flows. In a first part, two dominant classes of techniques for extracting Lagrangian Coherent Structures are reviewed and compared and some improvements are suggested for their pragmatic applications on realistic high-dimensional deterministic ocean velocity fields. In the stochastic case, estimating the uncertain Lagrangian motion can require to evaluate an ensemble of realizations of the flow map associated with a random velocity flow field, or equivalently realizations of the solution of a related transport partial differential equation. The Dynamically Orthogonal (DO) approximation is applied as an efficient model order reduction technique to solve this stochastic advection equation. With the goal of developing new rigorous reduced-order advection schemes, the second part of this work investigates the mathematical foundations of the method. Riemannian geometry providing an appropriate setting, a framework free of tensor notations is used to analyze the embedded geometry of three popular matrix manifolds, namely the fixed rank manifold, the Stiefel manifold and the isospectral manifold. Their extrinsic curvatures are characterized and computed through the study of the Weingarten map. As a spectacular by-product, explicit formulas are found for the differential of the truncated Singular Value Decomposition, of the Polar Decomposition, and of the eigenspaces of a time dependent symmetric matrix. Convergent gradient flows that achieve related algebraic operations are provided. A generalization of this framework to the non-Euclidean case is provided, allowing to derive analogous formulas and dynamical systems for tracking the eigenspaces of non-symmetric matrices. In the geometric setting, the DO approximation is a particular case of projected dynamical systems, that applies instantaneously the SVD truncation to optimally constrain the rank of the reduced solution. It is obtained that the error committed by the DO approximation is controlled under the minimal geometric condition that the original solution stays close to the low-rank manifold. The last part of the work focuses on the practical implementation of the DO methodology for the stochastic advection equation. Fully linear, explicit central schemes are selected to ensure stability, accuracy and efficiency of the method. Riemannian matrix optimization is applied for the dynamic evaluation of the dominant SVD of a given matrix and is integrated to the DO time-stepping. Finally the technique is illustrated numerically on the uncertainty quantification of the Lagrangian motion of two bi-dimensional benchmark flows.
by Florian Feppon.
S.M.
Bizi, Nadir. "Semi-riemannian noncommutative geometry, gauge theory, and the standard model of particle physics." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS413/document.
Full textThe subject of this thesis is noncommutative geometry - more specifically spectral triples - and how it can be used to unify General Relativity with the Standard Model of particle physics. This unification has already been achieved with spectral triples for Riemannian manifolds. The main concern of this thesis is to generalize this construction to semi-Riemannian manifolds generally, and Lorentzian manifolds in particular. The first half of this thesis will thus be dedicated to the transition from Riemannian to semi-Riemannian manifolds. This entails a study of Clifford algebras for indefinite vector spaces and Spin structures on semi-Riemannian manifolds. An important consequence of this is the introduction of complex vector spaces of indefinite signature. These are the so-called Krein spaces, which will enable us to generalize spectral triples to indefinite spectral triples. In the second half of this thesis, we will apply the formalism of noncommutative differential forms to indefinite spectral triples to construct noncommutative gauge theories on Lorentzian spacetimes. We will then demonstrate how to recover the Standard Model
Baspinar, Emre <1988>. "Minimal Surfaces in Sub-Riemannian Structures and Functional Geometry of the Visual Cortex." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amsdottorato.unibo.it/8661/7/thesis_baspinar_for_submission.pdf.
Full textRupassara, Rupassarage Upul Hemakumara. "Joint exit time and place distribution for Brownian motion on Riemannian manifolds." OpenSIUC, 2019. https://opensiuc.lib.siu.edu/dissertations/1720.
Full textMcMahon, Joseph Brian. "Geometry and Mechanics of Growing, Nonlinearly Elastic Plates and Membranes." Diss., The University of Arizona, 2009. http://hdl.handle.net/10150/194028.
Full textLeijon, Rasmus. "The Einstein Field Equations : on semi-Riemannian manifolds, and the Schwarzschild solution." Thesis, Umeå universitet, Institutionen för matematik och matematisk statistik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-61321.
Full textCheung, Leung-Fu. "Geometric properties of stable noncompact constant mean curvature surfaces." Bonn : [s.n.], 1991. http://catalog.hathitrust.org/api/volumes/oclc/26531351.html.
Full textHainz, Stefan. "Eine Riemannsche Betrachtung des Reeb-Flusses." Bonn : Mathematisches Institut der Universität, 2006. http://catalog.hathitrust.org/api/volumes/oclc/173261156.html.
Full textReach, Andrew McCaleb. "Smooth Interactive Visualization." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/78848.
Full textPh. D.
ROITBERG, ALICE. "Gross-Pitaevskii hydrodynamics in Riemannian manifolds and application in Black Hole cosmology." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2023. https://hdl.handle.net/10281/404710.
Full textIn this thesis we analyze the physical implications of the geometry of the ambient space in the context of Bose-Einstein condensates (BECs) and possible applications to the field of analogue models in the cosmology of black holes. To this end we derive the hydrodynamic formulation of the Gross-Pitaevskii equation (GPE) in the case of a generic Riemannian manifold. We observe the appearance of a new force, which essentially depends on two parameters: the geometry of the manifold and the first derivatives of the density profile. The stationary conditions are studied in relation to the presence of manifolds with negative scalar curvature. By analyzing these manifolds, an explicit relationship is established between the negatively curved surfaces and the sine-Gordon equation, which results in an approximation of the GPE in the presence of phase coupling. By assuming stationary conditions, we obtain a new type of Einstein field equations and we look for other possible connections between the equations governing condensates and cosmology. For this purpose, we consider relativistic BECs, that are used in the study of the early universe and its expansion, and we obtain Einstein equation in the multi-dimensional case. Then we consider the analogue models used for the study of the formation of black holes and for the calculation of Hawking radiation. Through a linearization process it is possible to derive a Lorentzian acoustic metric for the phase fluctuations; for this purpose, we consider the case of a straight vortex defect with a density profile where the first derivatives have maximum value inside the vortex tube and the geometry of the ambient space becomes relevant. In this situation it turns out that it is possible to determine a Lorentzian metric, and some useful approximations are proposed for its explicit computation. Finally, some concluding remarks are presented on possible future research directions, given by the study of the evolution of isophase surfaces in relativistic cases, and the study of condensates subject to twist.
Tashiro, Kenshiro. "Gromov-Hausdorff limits of compact Heisenberg manifolds with sub-Riemannian metrics." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263433.
Full textRuscelli, Francesco. "On the Palatini formulation of general relativity." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/23693/.
Full textRöttgen, Nena-Maria [Verfasser], and Victor [Akademischer Betreuer] Bangert. "Existence of periodic orbits in Riemannian and contact geometry = Existenz periodischer Orbits in Riemannscher und Kontaktgeometrie." Freiburg : Universität, 2014. http://d-nb.info/1123482098/34.
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