• Data-Driven Robust Control Using Reinforcement Learning 

      Ngo, Phuong; Tejedor Hernandez, Miguel Angel; Godtliebsen, Fred (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-02-21)
      This paper proposes a robust control design method using reinforcement learning for controlling partially-unknown dynamical systems under uncertain conditions. The method extends the optimal reinforcement learning algorithm with a new learning technique based on the robust control theory. By learning from the data, the algorithm proposes actions that guarantee the stability of the closed-loop system ...
    • De-identifying Swedish EHR text using public resources in the general domain 

      Chomutare, Taridzo; Yigzaw, Kassaye Yitbarek; Budrionis, Andrius; Makhlysheva, Alexandra; Godtliebsen, Fred; Dalianis, Hercules (Journal article; Tidsskriftartikkel; Peer reviewed, 2020)
      Sensitive data is normally required to develop rule-based or train machine learning-based models for de-identifying electronic health record (EHR) clinical notes; and this presents important problems for patient privacy. In this study, we add non-sensitive public datasets to EHR training data; (i) scientific medical text and (ii) Wikipedia word vectors. The data, all in Swedish, is used to train a ...
    • Decomposable (5, 6)-solutions in eleven-dimensional supergravity 

      Chi, Hanci; Chrysikos, Ioannis; Schneider, Eivind (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-06-08)
      We present decomposable (5, 6)-solutions M<sup>1,4</sup>×M<sup>6</sup> in eleven-dimensional supergravity by solving the bosonic supergravity equations for a variety of non-trivial flux forms. Many of the bosonic backgrounds presented here are induced by various types of null flux forms on products of certain totally Ricci-isotropic Lorentzian Walker manifolds and Ricci-flat Riemannian manifolds. ...
    • Deep learning applied to fish otolith images 

      Martinsen, Iver (Master thesis; Mastergradsoppgave, 2021-11-14)
      This thesis is concerned with classification and regression using deep learning applied to fish otolith images. Otoliths (earstones) are calcified structures in the inner ear of vertebrates, and are used, for instance, in fish stock assessment and fish age determination. We use convolutional neural networks – a class of deep learning models - on two specific problems: discrimination between Northeast ...
    • Deep Learning Based Automatic Segmentation of Gas Flares in Single Beam Echo Sounder Data 

      Skotnes, Teodor Lynghaug (Mastergradsoppgave; Master thesis, 2024-01-18)
      This thesis introduces the first study of instance segmentation applied to gas flares in single beam echo sounder data. We develop a comprehensive dataset consisting of 1,414 images, featuring 5,142 segmented objects identified as gas flare. A key contribution is the adaptation of the Brier score specifically for instance segmentation. Further, we show how to adapt the Weighted Box Fusion (WBF) ...
    • Deformation of big pseudoholomorphic disks and application to the Hanh pseudonorm 

      Kruglikov, Boris (Journal article; Tidsskriftartikkel; Peer reviewed, 2003-04-14)
      We simplify proof of the theorem that close to any pseudoholomorphic disk there passes a pseudoholomorphic disk of arbitrary close size with any pre-described sufficiently close direction. We apply these results to the Kobayashi and Hanh pseudodistances. It is shown they coincide in dimensions higher than four. The result is new even in the complex case.
    • Deforming the vacuum. On the physical origin and numerical calculation of the Casimir effect. 

      Mikalsen, Karl Øyvind (Master thesis; Mastergradsoppgave, 2014-05-14)
      A new method for calculating the Casimir force between compact objects was introduced in May 2012 by Per Jakobsen and Isak Kilen. In this method a regularization procedure is used to reduce the pressure to the solution of an integral equation defined on the boundaries of the objects. In this thesis the method is further developed by extending from a 2D to a 3D massless scalar field, subject to ...
    • DeltaProt : a software toolbox for comparative genomics 

      Thorvaldsen, Steinar; Flå, Tor; Willassen, Nils P (Journal article; Tidsskriftartikkel; Peer reviewed, 2010)
    • Density ridge manifold traversal 

      Myhre, Jonas Nordhaug; Kampffmeyer, Michael C.; Jenssen, Robert (Chapter; Bokkapittel, 2017-06-19)
      The density ridge framework for estimating principal curves and surfaces has in a number of recent works been shown to capture manifold structure in data in an intuitive and effective manner. However, to date there exists no efficient way to traverse these manifolds as defined by density ridges. This is unfortunate, as manifold traversal is an important problem for example for shape estimation in ...
    • Differential invariants of the 2D conformal Lie algebra action 

      Høyem, Marte Rørvik (Master thesis; Mastergradsoppgave, 2008-02-15)
      In this thises we consider the Lie algebra that corresponds to the Lie pseudogroup of all conformal transformations on the plane. This conformal Lie algebra is canonically represented as a Lie algebra of vector fields on R^2. We will find all possible representations of vector fields in R^3=J^0R^2 which projects to the canonical representation and find the algebra of scalar differential invariants ...
    • Differential invariants of curves in G2 flag varieties 

      Kruglikov, Boris; Llabrés, Andreu (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-05-10)
      We compute the algebra of differential invariants of unparametrized curves in the homogeneous G<sub>2</sub> flag varieties, namely in G<sub>2</sub>/P. This gives a solution to the equivalence problem for such curves. We consider the cases of integral and generic curves and relate the equivalence problems for all three choices of the parabolic subgroup P.
    • Differential invariants of Einstein-Weyl structures in 3D 

      Kruglikov, Boris; Schneider, Eivind (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-05-22)
      Einstein–Weyl structures on a three-dimensional manifold <i>M</i> are given by a system <i>E</i> of PDEs on sections of a bundle over <i>M</i>. This system is invariant under the Lie pseudogroup <i>G</i> of local diffeomorphisms on <i>M</i>. Two Einstein–Weyl structures are locally equivalent if there exists a local diffeomorphism taking one to the other. Our goal is to describe the quotient equation ...
    • Differential invariants of Kundt spacetimes 

      Kruglikov, Boris; Schneider, Eivind (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-09-07)
      We find generators for the algebra of rational differential invariants for general and degenerate Kundt spacetimes and relate this to other approaches to the equivalence problem for Lorentzian metrics. Special attention is given to dimensions three and four.
    • Differential invariants of Kundt waves 

      Kruglikov, Boris; McNutt, David Duncan; Schneider, Eivind (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-07-17)
      Kundt waves belong to the class of spacetimes which are not distinguished by their scalar curvature invariants. We address the equivalence problem for the metrics in this class via scalar differential invariants with respect to the equivalence pseudo-group of the problem. We compute and finitely represent the algebra of those on the generic stratum and also specify the behavior for vacuum Kundt ...
    • Differential Invariants of Linear Symplectic Actions 

      Jensen, Jørn Olav; Kruglikov, Boris (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-12-07)
      We consider the equivalence problem for symplectic and conformal symplectic group actions on submanifolds and functions of symplectic and contact linear spaces. This is solved by computing differential invariants via the Lie-Tresse theorem.
    • Differential invariants of self-dual conformal structures 

      Kruglikov, Boris; Schneider, Eivind (Journal article; Tidsskriftartikkel; Peer reviewed, 2016-06-17)
      We compute the quotient of the self-duality equation for conformal metrics by the action of the diffeomorphism group. We also determine Hilbert polynomial, counting the number of independent scalar differential invariants depending on the jet-order, and the corresponding Poincaré function. We describe the field of rational differential invariants separating generic orbits of the diffeomorphism ...
    • Differential Invariants of Symplectic and Contact Lie Algebra Actions 

      Jensen, Jørn Olav (Master thesis; Mastergradsoppgave, 2020-06-23)
      In this thesis we consider the equivalence problem for symplectic and conformal symplectic group actions on submanifolds and functions. We solve the equivalence problem for general submanifolds by means of computing differential invariants and describing all the invariants of the associated group action by appealing to the Lie-Tresse theorem.
    • Differential invariants of the motion group actions 

      Kruglikov, Boris; Lychagin, Valentin V. (Working paper; Arbeidsnotat, 2007-12-20)
      Differential invariants of a (pseudo)group action can vary when restricted to invariant submanifolds (differential equations). The algebra is still governed by the Lie-Tresse theorem, but may change a lot. We describe in details the case of the motion group O(n) ⋉ R<sup>n</sup> acting on the full (unconstraint) jet-space as well as on some invariant equations.
    • Dimension of the solutions space of PDEs 

      Kruglikov, Boris; Lychagin, Valentin V. (Conference object; Konferansebidrag, 2006-10-26)
      We discuss the dimensional characterization of the solutions space of a formally integrable system of partial differential equations and provide certain formulas for calculations of these dimensional quantities.
    • Dirichlet process cluster kernel 

      Foslid, Tobias Olsen (Master thesis; Mastergradsoppgave, 2017-05-16)
      This thesis aims to apply the Dirichlet process mixture model to the cluster kernel framework. The probabilistic cluster kernel is extended with a Bayesian nonparametric model to avoid critical parameters within the model. The Dirichlet process cluster kernel demonstrate advantages compared to the probabilistic cluster kernel in both classification and clustering. Additionally, the two dimensional ...