Artikler, rapporter og annet (matematikk og statistikk)
Browse by
Recent additions

On the degree of varieties of sum of squares
(Journal article; Tidsskriftartikkel; Peer reviewed, 20240210)We study the problem of how many different sum of squares decompositions a general polynomial <i>f</i> with SOSrank <i>k</i> admits. We show that there is a link between the variety SOS<sub><i>k</sub></i>(<i>f</i>) of all SOSdecompositions of <i>f</i> and the orthogonal group O(<i>k</i>). We exploit this connection to obtain the dimension of SOS<sub><i>k</sub></i>(<i>f</i>) and show that its degree ... 
The span of singular tuples of a tensor beyond the boundary format
(Journal article; Tidsskriftartikkel; Peer reviewed, 20230510)A singular <i>k</i>tuple of a tensor T of format (<i>n<sub>1</sub></i>, ..., <i>n</i><sub><i><k></i></sub>) is essentially a complex critical point of the distance function from <i>T</i> constrained to the cone of tensors of format (<i>n</i><sub>1</sub>, ..., <i>n<sub>k</sub></i>) of rank at most one. A generic tensor has finitely many complex singular <i>k</i>tuples, and their number depends only ... 
Generalized identifiability of sums of squares
(Journal article; Tidsskriftartikkel; Peer reviewed, 2025) 
Binary forms of suprageneric rank and the multiple root loci
(Journal article; Tidsskriftartikkel; Peer reviewed, 20230811)We state the relation between the variety of binary forms of given rank and the dual of the multiple root loci. This is a new result for the suprageneric rank that appears as a continuation of the cited work by Buczyński, Han, Mella and Teitler. We describe the strata of these varieties and explore their singular loci. 
The 3billion fossil question: How to automate classification of microfossils
(Journal article; Tidsskriftartikkel; Peer reviewed, 20240608)Microfossil classification is an important discipline in subsurface exploration, for both oil & gas and Carbon Capture and Storage (CCS). The abundance and distribution of species found in sedimentary rocks provide valuable information about the age and depositional environment. However, the analysis is difficult and timeconsuming, as it is based on manual work by human experts. Attempts to automate ... 
Disease activity trajectories from childhood to adulthood in the populationbased Nordic juvenile idiopathic arthritis cohort
(Journal article; Tidsskriftartikkel; Peer reviewed, 20240308)Objectives To identify longterm disease activity trajectories from childhood to adulthood by using the clinical Juvenile Arthritis Disease Activity Score (cJADAS10) in juvenile idiopathic arthritis (JIA). Second, to evaluate the contribution of the cJADAS10 components and explore characteristics associated with active disease at the 18 year followup.<p> <p>Methods Patients with onset of ... 
Orbit Spaces of Weyl Groups Acting on Compact Tori: A Unified and Explicit Polynomial Description
(Journal article; Tidsskriftartikkel; Peer reviewed, 2024)The Weyl group of a crystallographic root system has a multiplicative action on the compact torus. The orbit space of this action is a compact basic semialgebraic set. We present a polynomial description of this set for the Weyl groups associated to root systems of types A, B, C, D and G. Our description is given through a polynomial matrix inequality. The novelty lies in an approach via Hermite ... 
Symmetries in Polynomial Optimization
(Chapter; Bokkapittel, 20231228)This chapter investigates how symmetries can be used to reduce the computational complexity in polynomial optimization problems. A focus will be specifically given on the MomentSOS hierarchy in polynomial optimization, where results from representation theory and invariant theory of groups can be used. In addition, symmetry reduction techniques which are more generally applicable are also presented. 
Increasing fluctuations in the Arctic summer sea ice cover are expected with future global warming
(Journal article; Tidsskriftartikkel; Peer reviewed, 20240611)The loss of Arctic sea ice (ASI) represents a major transformation in the Arctic region, impacting regional and global climate, ecosystems, and socioeconomic structures. Observational and reanalysis data have consistently shown a notable shift in polar environmental conditions over recent decades, marked by a substantial reduction in the ASI area and a rise in the variability in its coverage and ... 
Arctic summer sea ice loss will accelerate in coming decades
(Journal article; Tidsskriftartikkel; Peer reviewed, 20240617)The Arctic sea ice (ASI) is expected to decrease with further global warming. However, considerable uncertainty remains regarding the temperature range that would lead to a completely icefree Arctic. Here, we combine satellite data and a large suite of models from the latest phase of the Coupled Model Intercomparison Project (CMIP6) to develop an empirical, observationbased projection of the ... 
Beyond the OberbeckBoussinesq and long wavelength approximation
(Journal article; Tidsskriftartikkel, 20221222)We present the first simulations of a reduced magnetized plasma model that incorporates both arbitrary wavelength polarization and nonOberbeck–Boussinesq effects. Significant influence of these two effects on the density, electric potential and <i><b>E</i></b> × <i><b>B</i></b> vorticity and nonlinear dynamics of interchange blobs are reported. Arbitrary wavelength polarization implicates socalled ... 
On uniqueness of submaximally symmetric parabolic geometries
(Journal article; Tidsskriftartikkel; Peer reviewed, 20240124)Among (regular, normal) parabolic geometries of type (<i>G,P</i>), there is a locally unique maximally symmetric structure and it has symmetry dimension dim(<i>G</i>). The symmetry gap problem concerns the determination of the next realizable (submaximal) symmetry dimension. When <i>G</i> is a complex or splitreal simple Lie group of rank at least three or when (<i>G,P</i>) = (<i>G<sub>2</sub></i>, ... 
Preservice and inservice teachers’ views on digital tools for diverse learners in mathematics education
(Journal article; Tidsskriftartikkel; Peer reviewed, 2023)Although teachers are expected to use digital tools in their mathematics teaching in many countries, little is known about preservice and inservice teachers’ digital competence, especially in relationship to specific groups of school students. Results from a survey of 394 preservice teachers and 61 inservice teachers, at three Norwegian institutions, provide information on how they considered different ... 
Biogeographic gradients of picoplankton diversity indicate increasing dominance of prokaryotes in warmer Arctic fjords
(Journal article; Tidsskriftartikkel; Peer reviewed, 20240302)limate change is opening the Arctic Ocean to increasing human impact and ecosystem changes. Arctic fjords, the region’s most productive ecosystems, are sustained by a diverse microbial community at the base of the food web. Here we show that Arctic fjords become more prokaryotic in the picoplankton (0.2–3 µm) with increasing water temperatures. Across 21 fjords, we found that Arctic fjords had ... 
Linear codes associated to symmetric determinantal varieties: Even rank case
(Journal article; Tidsskriftartikkel; Peer reviewed, 20230620)We consider linear codes over a finite field Fq, for odd q, derived from determinantal varieties, obtained from symmetric matrices of bounded ranks. A formula for the weight of a codeword is derived. Using this formula, we have computed the minimum distance for the codes corresponding to matrices upperbounded by any fixed, even rank. A conjecture is proposed for the cases where the upper bound is ... 
Exceptionally simple superPDE for F (4)
(Journal article; Tidsskriftartikkel; Peer reviewed, 20240201)For the largest exceptional simple Lie superalgebra F(4), having dimension (2416), we provide two explicit geometric realizations as supersymmetries, namely as the symmetry superalgebra of superPDE systems of second and third order respectively. 
ODEs whose Symmetry Groups are not FiberPreserving
(Journal article; Tidsskriftartikkel; Peer reviewed, 2023)We observe that, up to conjugation, a majority of higher order ODEs (ordinary differential equations) and ODE systems have only fiberpreserving point symmetries. By exploiting Lie's classification of Lie algebras of vector fields, we describe all exceptions to this in the case of scalar ODEs and systems of ODEs on a pair of functions. The scalar ODEs whose symmetry algebras are not fiber preserving ... 
Decomposable (5, 6)solutions in elevendimensional supergravity
(Journal article; Tidsskriftartikkel; Peer reviewed, 20230608)We present decomposable (5, 6)solutions M<sup>1,4</sup>×M<sup>6</sup> in elevendimensional supergravity by solving the bosonic supergravity equations for a variety of nontrivial flux forms. Many of the bosonic backgrounds presented here are induced by various types of null flux forms on products of certain totally Ricciisotropic Lorentzian Walker manifolds and Ricciflat Riemannian manifolds. ... 
Power availability of PV plus thermal batteries in realworld electric power grids
(Journal article; Tidsskriftartikkel; Peer reviewed, 20230725)As variable renewable energy sources comprise a growing share of total electricity generation, energy storage technologies are becoming increasingly critical for balancing energy generation and demand.<p> <p>In this study, a realworld electricity system was modeled rather than modeling hypothetical future electric power systems where the existing electricity infrastructure are neglected. In ... 
The expressive power of pooling in Graph Neural Networks
(Journal article; Tidsskriftartikkel; Peer reviewed, 2023)In Graph Neural Networks (GNNs), hierarchical pooling operators generate local summaries of the data by coarsening the graph structure and the vertex features. While considerable attention has been devoted to analyzing the expressive power of messagepassing (MP) layers in GNNs, a study on how graph pooling affects the expressiveness of a GNN is still lacking. Additionally, despite the recent advances ...