View source for Biography:Alfréd Haar

{{short description|Hungarian mathematician}}
{{Infobox scientist
|name  = Alfréd Haar
|image = Haar Alfréd.jpg
|birth_date = 11 October 1885
|birth_place = [[Place:Budapest|Budapest]], [[History:Kingdom of Hungary|Kingdom of Hungary]]
|death_date = {{death date and age|1933|03|16|1885|10|11|df=yes}}
|death_place = Szeged, [[History:Kingdom of Hungary (1920–1946)|Hungary]]
|nationality = Hungarian
|fields = [[Mathematics]]
|workplaces = Franz Joseph University<br>University of Szeged
|alma_mater = University of Göttingen
|known_for        =  [[Haar measure]]<br>[[Haar space]]<br>Haar transform<br>[[Haar wavelet]]<br>[[Haar's Tauberian theorem]]
|doctoral_advisor = [[Biography:David Hilbert|David Hilbert]]
|doctoral_students = Béla Szőkefalvi-Nagy
}}

'''Alfréd Haar''' ({{lang-hu|Haar Alfréd}}; 11 October 1885, [[Place:Budapest|Budapest]]&nbsp;&ndash; 16 March 1933, Szeged) was a [[History:Kingdom of Hungary|Hungarian]] [[Biography:Mathematician|mathematician]]. In 1904 he began to study at the University of Göttingen. His doctorate was supervised by [[Biography:David Hilbert|David Hilbert]]. The [[Haar measure]], [[Haar wavelet]], and Haar transform are named in his honor. Between 1912 and 1919 he taught at Franz Joseph University in Kolozsvár. Together with [[Biography:Frigyes Riesz|Frigyes Riesz]], he made the University of Szeged a centre of mathematics. He also founded the ''[[Acta Scientiarum Mathematicarum]]'' journal together with Riesz.

== Biography ==
[[File:Matematikai konferencia Szegeden, 1928.jpg|thumb|Conference at the University of Szeged, 1928. ''Left to right, standing:'' Frigyes Riesz, Béla Kerékjártó, Alfréd Haar, Gyula Kőnig, {{Interlanguage link multi|Rudolf Ortvay|hu|3=Ortvay Rudolf}}, ''on chairs:'' József Kürschák, George David Birkhoff, O.D. Kellog, Leopold Fejér, ''sitting on the floor:'' Tibor Radó, {{Interlanguage link multi|István Lipka|hu|3=Lipka István}}, László Kalmár, {{Interlanguage link multi|Pál Szász|hu|3=Szász Pál (matematikus)}}]]
Haar was born to a Hungarian-Jewish<ref>''Transcending Tradition: Jewish Mathematicians in German Speaking Academic Culture'', Birgit Bergmann, (Springer 2012), page 63</ref> family in Budapest on 11 October 1885 to parents Ignác Haar and Emma Fuchs. He graduated in 1903 from the secondary school Fasori Evangélikus Gimnázium where he was a student of László Rátz. He started his university studies in Budapest, later moving on to Göttingen reading mathematics and sciences. Among the many famous professors he was taught by, he could count [[Biography:Loránd Eötvös|Loránd Eötvös]], József Kürschák, [[Biography:Constantin Carathéodory|Constantin Carathéodory]], [[Biography:David Hilbert|David Hilbert]], Felix Christian Klein and [[Biography:Ernst Zermelo|Ernst Zermelo]].

During years of the secondary school, he collaborated with the mathematical journal for secondary school students Középiskolai Matematikai Lapok, and won the national Eötvös Loránd Mathematical Competition. He enrolled to the Technical University of Budapest as a student of chemical engineering, but in the same year he moved on to the University of Budapest, and after a year to the University of Göttingen. His doctoral research was supervised by Hilbert graduating in June 1909. His 49-page thesis studies systems of [[Sturm–Liouville theory|Sturm–Liouville function]]s and [[Zonal spherical function|spherical function]]s, introducing the now widely used Haar orthogonal systems. In the same year he habilitated to become a private professor of the university.

In 1912, the Franz Joseph University in Kolozsvár, [[Place:Austria-Hungary|Austria-Hungary]] (now Cluj-Napoca in Romania) invited him along with Gyula Farkas and [[Biography:Frigyes Riesz|Frigyes Riesz]] to join as faculty, and he became the professor of 'Quatitics'. A number of his lecture notes from the time became established books later. After the Treaty of Trianon, which ceded [[Place:Transylvania|Transylvania]] to Romania, the university had to move to Szeged, the closest city within the new boundaries, where he with Riesz established the Centre of Mathematics, and the first internationally recognised Hungarian mathematical journal, the ''Acta Scientiarum Mathematicarum''.

One of his doctoral students at the University of Szeged was [[Biography:Béla Szőkefalvi-Nagy|Béla Szőkefalvi-Nagy]].

Haar died of stomach cancer on 16 March 1933.

== Fields of research ==
His results are from the fields of [[Mathematical analysis|mathematical analysis]] and [[Topological group|topological group]]s, in particular he researched [[Orthogonal functions|orthogonal systems of functions]], [[Singular integral|singular integral]]s, analytic functions, differential equations, [[Set theory|set theory]], [[Function approximation|function approximation]] and [[Calculus of variations|calculus of variations]].

== Publications ==
* Haar, A., ''[https://link.springer.com/article/10.1007/BF01456326   Zur Theorie der orthogonalen Funktionensysteme]'', (''Erste Mitteilung''), [[Mathematische Annalen|Math. Ann.]] 69 (1910), 331–371 (at GDZ). (This is Haar's thesis, written under the supervision of David Hilbert.)
* Haar, A., ''[https://link.springer.com/article/10.1007%2FBF01457106  Die Minkowskische Geometrie und die Annäherung an stetige Funktionen]'', Math. Ann. 78 (1918), 294–311 (at GDZ).

== References ==
<references />

== External links ==
* {{MacTutor Biography|id=Haar}}
* {{MathGenealogy|id=7375}}.
* {{DNB-Portal|116346590}}.

{{DEFAULTSORT:Haar, Alfred}}
[[Category:Measure theorists]]

{{Sourceattribution|Alfréd Haar}}