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28 results on '"Njåstad, O."'

14. Orthogonal rational functions on the real half line with poles in [-infinity, 0]

Author

Bultheel, A., Gonzalez-Vera, P., Hendriksen, E., Njåstad, O., and Analysis (KDV, FNWI)

Abstract

The main objective is to generalize previous results obtained for orthogonal Laurent polynomials and their application in the context of Stieltjes moment problems to the multipoint case. The measure of orthogonality is supposed to have support on [0, infinity) while the orthogonal rational functions will have poles that are assumed to be "in the neighborhood of 0 and infinity". In this way orthogonal Laurent polynomials will be a special case obtained when all the poles are at 0 and infinity. We shall introduce the restrictions on the measure and the locations of the poles gradually and derive recurrence relations, Christoffel-Darboux relations, and the solution of the rational Stieltjes moment problem under appropriate conditions.

Published
2005

15. Separation of zeros of para-orthogonal rational functions

Author

Bultheel, A., Gonzalez-Vera, P., Hendriksen, E., Njåstad, O., and Analysis (KDV, FNWI)

Abstract

We generalize a result by L. Golinskii¹ on separation of the zeros of para-orthogonal polynomials on the unit circle to a similar result for para-orthogonal rational functions. ¹ L. Golinskii, Quadrature formula and zeros of para-orthogonal polynomials on the unit circle, Acta Math. Hungar. 96 169-186, 2002. ispartof: Revista de la Academia Canaria de Ciencias vol:16 issue:1 pages:9-14 status: published

Published
2005

20. Parasuicide in the Nordic countries.

Author

Wasserman, D, Fellman, M, Bille-Brahe, U, Bjerke, T, Jacobsson, Lars, Jessen, G, Lönnqvist, J K, Njåstad, O, Ostamo, A, Salander Renberg, Ellinor, Wasserman, D, Fellman, M, Bille-Brahe, U, Bjerke, T, Jacobsson, Lars, Jessen, G, Lönnqvist, J K, Njåstad, O, Ostamo, A, and Salander Renberg, Ellinor

Abstract

This article gives an account of some findings of the WHO/EURO multicentre study on parasuicide from the five Nordic centres: Helsinki (Finland), Stockholm (Sweden), and the countries of Funen (Denmark), Sø-Trøndelag (Norway) and Västerbotten (Sweden). For parasuicide patients treated in hospital in these five Nordic centres, the parasuicide rates per 100,000 inhabitants per annum were 222 for women, 213 for men and 224 for both sexes combined. In all the Nordic centres except Helsinki, women had higher parasuicide rates than men. The female/male parasuicide ratio was 1.16 for all Nordic centres. The highest parasuicide rates in the whole material were found in Helsinki, Stockholm and Funen, and the lowest in Sør-Trøndelag and Västerbotten. The highest parasuicide rates lay in the 30-39 age interval, i.e. the peak of parasuicide rates was in older age groups than previously reported. Single people, especially divorcees and those who have never been married, constitute a high-risk group in both sexes. The risk of parasuicide for single men is three times that for married men in all the Nordic centres except Sør-Trøndelag, where the risk is five times higher. The parasuicide risk for single women is twice as high as for married women except for women in Funen, where the risk for single and married women is almost equal. Exceptionally high parasuicide rates are also reported for Finnish citizens in Sweden, compared with Finns from the Helsinki centre. Parasuicide rates appear to be correlated with population density, since the densely populated areas of Helsinki, Stockholm and Funen evince higher parasuicide rates than the sparsely populated areas of Sør-Trøndelag and Västerbotten.

Published
1994

26. Orthogonal rational functions on the real half line with poles in [-∞,0]

Author

Bultheel, A., González-Vera, P., Hendriksen, E., and Njåstad, O.

Subjects
Rational Stieltjes problem, Orthogonal rational functions, Quadrature formulas
Abstract

The main objective is to generalize previous results obtained for orthogonal Laurent polynomials and their application in the context of Stieltjes moment problems to the multipoint case. The measure of orthogonality is supposed to have support on [0,∞) while the orthogonal rational functions will have poles that are assumed to be “in the neighborhood of 0 and ∞”. In this way orthogonal Laurent polynomials will be a special case obtained when all the poles are at 0 and ∞. We shall introduce the restrictions on the measure and the locations of the poles gradually and derive recurrence relations, Christoffel–Darboux relations, and the solution of the rational Stieltjes moment problem under appropriate conditions.

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27. Interpolation by Rational Functions with Nodes on the Unit Circle

Author

Adhemar Bultheel, González-Vera, P., Hendriksen, E., Njåstad, O., and Analysis (KDV, FNWI)

Subjects
convergence, orthogonal rational functions, quadrature-formulas, interpolation, r-Szego quadrature
Abstract

From the Erdös-Turán theorem, it is known that if f is a continuous function on T={z:|z|=1} and L_n(f,z) denotes the unique Laurent polynomial interpolating f at the (2n+1)th roots of unity, then lim_{n→∞} ∫_T |f(z)-L_n(f,z)|^2| |d z|=0. Several years later, Walsh and Sharma gave a similar result but now considering a function analytic in D={z:|z

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