Person: Norlund, Niels Erik
Niels Norlund was a Danish mathematician and astronomer who worked in the theory of difference equations.
Mathematical Profile (Excerpt):
 Niels attended elementary school in Slagelse but then had to go to the larger nearby town of Soro for his secondary schooling.
 At school Norlund had loved mathematics and astronomy.
 Norlund was most attracted by the vigorous Niels Nielsen, who lectured on the theory of functions, and by Thorvald Thiele whose interests in astronomy were mainly on orbits and the threebody problem.
 Norlund's first publication was in 1905 when he published a paper on a known double star in Ursa Major which, with careful measurements of their orbits, he was able to deduce was actually a triple system with a third star which was too faint to observe.
 In addition to spending considerable time observing star positions and proper motions of stars, Norlund also undertook research in mathematics.
 These publications in the most prestigious French journal earned Norlund an international reputation despite still being an undergraduate.
 Following the award of his doctorate, Norlund remained at Copenhagen for two years continuing to work as an assistant at the Observatory.
 In particular the little paper 'Sur une application des fonctions permutables' Ⓣ(On an application of permutable functions) from 1919 should be mentioned: there he states some universal results on the summability of series based on a specific  but rather general  choice of the weights given to the elements; the method includes the better of the known summability methods, such as Cesaro's method, and is now known under the standard designation of Norlundsummation.
 With a high international profile, Norlund was elected to the Danish Academy of Sciences in 1916.
 To solve this situation a third mathematics chair was created at the University of Copenhagen and Norlund invited to fill it.
 Events conspired to stop Norlund carrying out mathematical research during the thirty years he held the mathematics chair in Copenhagen.
 Norlund received a large number of honours for his contributions to mathematics and to geodesy.
Born 26 October 1885, Slagelse, near Soro, Sjaelland, Denmark. Died 4 July 1981, Copenhagen, Denmark.
View full biography at MacTutor
Tags relevant for this person:
Astronomy, Origin Denmark
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References
Adapted from other CC BYSA 4.0 Sources:
 O’Connor, John J; Robertson, Edmund F: MacTutor History of Mathematics Archive