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Hurwitz spaces of genus 2 covers of an elliptic curve.

Ernst Kani (2003)

Collectanea Mathematica

Let E be an elliptic curve over a field K of characteristic not equal to 2 and let N > 1 be an integer prime to char(K). The purpose of this paper is to construct the (two-dimensional) Hurwitz moduli space H (E/K,N,2) which classifies genus 2 covers of E of degree N and to show that it is closely related to the modular curve X(N) which parametrizes elliptic curves with level-N-structure. More precisely, we introduce the notion of a normalized genus 2 cover of E/K and show that the corresponding...

Hvězdicové mnohoúhelníky

Jan Fiala (2016)

Učitel matematiky

The article presents some possibilities to create non-convex star polygons from regular polygons. The text includes exercises about the construction of the star polygons and exercises inciting to study their attributes and their using in the everyday life of the pupil. The subject of the star polygons deepens the basic curriculum in plane geometry in RVP and it is a suitable motivation complement in teaching mathematics at the second stage of elementary school as well as at grammar school.

Hyperelliptic action integral

Bernhard Elsner (1999)

Annales de l'institut Fourier

Applying the “exact WKB method” (cf. Delabaere-Dillinger-Pham) to the stationary one-dimensional Schrödinger equation with polynomial potential, one is led to a multivalued complex action-integral function. This function is a (hyper)elliptic integral; the sheet structure of its Riemann surface above the plane of its values has interesting properties: the projection of its branch-points is in general a dense subset of the plane, and there is a group of symmetries acting on the surface. The distribution...

Ideal arithmetic and infrastructure in purely cubic function fields

Renate Scheidler (2001)

Journal de théorie des nombres de Bordeaux

This paper investigates the arithmetic of fractional ideals of a purely cubic function field and the infrastructure of the principal ideal class when the field has unit rank one. First, we describe how irreducible polynomials decompose into prime ideals in the maximal order of the field. We go on to compute so-called canonical bases of ideals; such bases are very suitable for computation. We state algorithms for ideal multiplication and, in the case of unit rank one and characteristic at least five,...

Improvement of Grauert-Riemenschneider's theorem for a normal surface

Jean Giraud (1982)

Annales de l'institut Fourier

Let X ˜ be a desingularization of a normal surface X . The group Pic ( X ˜ ) is provided with an order relation L _ 0 , defined by L . V 0 for any effective exceptional divisor V . Comparing to the usual order relation we define the ceiling of L which is an exceptional divisor. This notion allows us to improve the usual vanishing theorem and we deduce from it a numerical criterion for rationality and a genus formula for a curve on a normal surface; the difficulty lies in the case of a Weil divisor which is not a Cartier...

Indecomposable parabolic bundles

William Crawley-Boevey (2004)

Publications Mathématiques de l'IHÉS

We study the possible dimension vectors of indecomposable parabolic bundles on the projective line, and use our answer to solve the problem of characterizing those collections of conjugacy classes of n×n matrices for which one can find matrices in their closures whose product is equal to the identity matrix. Both answers depend on the root system of a Kac-Moody Lie algebra. Our proofs use Ringel’s theory of tubular algebras, work of Mihai on the existence of logarithmic connections, the Riemann-Hilbert...

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