Pál Turán

Pál Turán
Born	(1910-08-18)18 August 1910 Budapest, Austria-Hungary
Died	26 September 1976(1976-09-26) (aged 66) Budapest, Hungary
Nationality	Hungarian
Alma mater	University of Budapest
Known for	Power sum method Extremal graph theory
Awards	Kossuth Prize Tibor Szele Prize
Scientific career
Fields	Mathematics
Institutions	University of Budapest
Doctoral advisor	Lipót Fejér
Doctoral students	László Babai János Pintz

The native form of this personal name is Turán Pál. This article uses Western name order when mentioning individuals.

Pál Turán (Hungarian: [ˈpaːl ˈturaːn]; 18 August 1910 – 26 September 1976) also known as Paul Turán, was a Hungarian mathematician who worked primarily in number theory. He had a long collaboration with fellow Hungarian mathematician Paul Erdős, lasting 46 years and resulting in 28 joint papers.

Life and education

Turán was born into a Jewish family in Budapest on 18 August 1910.At the same period of time, Turán and Erdős were famous answerers in the journal KöMaL. He received a teaching degree at the University of Budapest in 1933 and the Ph.D. degree under Lipót Fejér in 1935 at Eötvös Loránd University.

As a Jew, he fell victim to numerus clausus, and could not get a university job for several years. He was sent to labour service at various times from 1940-44. He is said to have been recognized and perhaps protected by a fascist guard, who, as a mathematics student, had admired Turán's work.

Turán became associate professor at the University of Budapest in 1945 and full professor in 1949. Turán married Edit (Klein) Kóbor in 1939; they had one son, Róbert. Turán married, secondly, to Vera Sós, a mathematician, in 1952; they had two children, György and Tamás.

Death

Turán died in Budapest on 26 September 1976 of leukemia, aged 66.

Work

Turán worked primarily in number theory, but also did much work in analysis and graph theory.

Number theory

In 1934, Turán used the Turán sieve to give a new and very simple proof of a 1917 result of G. H. Hardy and Ramanujan on the normal order of the number of distinct prime divisors of a number n, namely that it is very close to $\ln \ln n$. In probabilistic terms he estimated the variance from $\ln \ln n$. Halász says "Its true significance lies in the fact that it was the starting point of probabilistic number theory". The Turán–Kubilius inequality is a generalization of this work.

Turán was very interested in the distribution of primes in arithmetic progressions, and he coined the term "prime number race" for irregularities in the distribution of prime numbers among residue classes. With his coauthor Knapowski he proved results concerning Chebyshev's bias. The Erdős–Turán conjecture makes a statement about primes in arithmetic progression. Much of Turán's number theory work dealt with the Riemann hypothesis and he developed the power sum method (see below) to help with this. Erdős said "Turán was an 'unbeliever,' in fact, a 'pagan': he did not believe in the truth of Riemann's hypothesis."

Analysis

Much of Turán's work in analysis was tied to his number theory work. Outside of this he proved Turán's inequalities relating the values of the Legendre polynomials for different indices, and, together with Paul Erdős, the Erdős–Turán equidistribution inequality.

Graph theory

Erdős wrote of Turán, "In 1940–1941 he created the area of extremal problems in graph theory which is now one of the fastest-growing subjects in combinatorics."Peter Frankl said of Turán, "He fell victim to Numerus clausus. Mathematicians have only paper and pen, he doesn't have anything in camp. So he created combinatorics which is not needed both thing."

The field is known more briefly today as extremal graph theory. Turán's best-known result in this area is Turán's Graph Theorem, that gives an upper bound on the number of edges in a graph that does not contain the complete graph K_r as a subgraph. He invented the Turán graph, a generalization of the complete bipartite graph, to prove his theorem. He is also known for the Kővári–Sós–Turán theorem bounding the number of edges that can exist in a bipartite graph with certain forbidden subgraphs, and for raising Turán's brick factory problem, namely of determining the crossing number of a complete bipartite graph.

Power sum method

Turán developed the power sum method to work on the Riemann hypothesis. The method deals with inequalities giving lower bounds for sums of the form

$\max _{\nu =m+1,\dots ,m+n}\left|\sum _{j=1}^{n}b_{j}z_{j}^{\nu }\right|,$ hence the name "power sum".

Aside from its applications in analytic number theory, it has been used in complex analysis, numerical analysis, differential equations, transcendental number theory, and estimating the number of zeroes of a function in a disk.

Publications

• Ed. by P. Turán. (1970). Number Theory. Amsterdam: North-Holland Pub. Co. ISBN 978-0-7204-2037-1.
• Paul Turán (1984). On a New Method of Analysis and Its Applications. New York: Wiley-Interscience. ISBN 978-0-471-89255-7. Deals with the power sum method.
• edited by Paul Erdős (1990). Collected Papers of Paul Turán. Budapest: Akadémiai Kiadó. ISBN 978-963-05-4298-2. {{cite book}}: |author= has generic name (help)

Honors

• Hungarian Academy of Sciences elected corresponding member in 1948 and ordinary member in 1953
• Kossuth Prize in 1948 and 1952
• Tibor Szele Prize of János Bolyai Mathematical Society 1975

External links

• O'Connor, John J.; Robertson, Edmund F., "Paul Turán", MacTutor History of Mathematics Archive, University of St Andrews
• Paul Turán memorial lectures at the Rényi Institute