Alf Van Der Poorten
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Alfred Jacobus (Alf) van der Poorten (16 May 1942 – 9 October 2010) was a Dutch-Australian
number theorist Number theory (or arithmetic or higher arithmetic in older usage) is a branch of pure mathematics devoted primarily to the study of the integers and integer-valued functions. German mathematician Carl Friedrich Gauss (1777–1855) said, "Mathe ...
, for many years on the mathematics faculties of the
University of New South Wales The University of New South Wales (UNSW), also known as UNSW Sydney, is a public research university based in Sydney, New South Wales, Australia. It is one of the founding members of Group of Eight, a coalition of Australian research-intensiv ...
and
Macquarie University Macquarie University ( ) is a Public university, public research university based in Sydney, Australia, in the suburb of Macquarie Park, New South Wales, Macquarie Park. Founded in 1964 by the New South Wales Government, it was the third univer ...
....


Biography

Van der Poorten was born into a Jewish family in Amsterdam in 1942, after the German occupation began. His parents, David and Marianne van der Poorten, gave him into foster care with the Teerink family in
Amersfoort Amersfoort () is a city and municipality in the province of Utrecht, Netherlands, about 20 km from the city of Utrecht and 40 km south east of Amsterdam. As of 1 December 2021, the municipality had a population of 158,531, making it the secon ...
, under the name "Fritsje"; the senior van der Poortens went into hiding, were caught by the Nazis, survived the
concentration camps Internment is the imprisonment of people, commonly in large groups, without charges or intent to file charges. The term is especially used for the confinement "of enemy citizens in wartime or of terrorism suspects". Thus, while it can simpl ...
, and were reunited with van der Poorten and his two sisters after the war. The family moved to Sydney in 1951, travelling there aboard the
SS Himalaya SS ''Himalaya'' was a British passenger ship of the Peninsular and Oriental Steam Navigation Company, launched in 1948, which operated mainly between Britain and Australia. She was withdrawn from service in 1974 and scrapped the next year. Histo ...
. Van der Poorten studied at
Sydney Boys High School , motto_translation = With Truth and Courage , established = , location = Cleveland Street, Moore Park, Sydney, New South Wales , country = Australia , coordinates = , p ...
from 1955–59, and earned a high score in the Leaving Certificate Examination there. He spent a year in
Israel Israel (; he, יִשְׂרָאֵל, ; ar, إِسْرَائِيل, ), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a country in Western Asia. It is situated ...
and then studied mathematics at the University of New South Wales, where he earned a bachelor's degree in 1965, a doctorate in 1968 under the joint supervision of
George Szekeres George Szekeres AM FAA (; 29 May 1911 – 28 August 2005) was a Hungarian–Australian mathematician. Early years Szekeres was born in Budapest, Hungary, as Szekeres György and received his degree in chemistry at the Technical University of ...
and
Kurt Mahler Kurt Mahler FRS (26 July 1903, Krefeld, Germany – 25 February 1988, Canberra, Australia) was a German mathematician who worked in the fields of transcendental number theory, diophantine approximation, ''p''-adic analysis, and the geometry o ...
, and a
Master of Business Administration A Master of Business Administration (MBA; also Master's in Business Administration) is a postgraduate degree focused on business administration. The core courses in an MBA program cover various areas of business administration such as accou ...
. While a student at UNSW, he led the student union council and was president of the University Union, as well as helping to lead several Jewish and
Zionist Zionism ( he, צִיּוֹנוּת ''Tsiyyonut'' after '' Zion'') is a nationalist movement that espouses the establishment of, and support for a homeland for the Jewish people centered in the area roughly corresponding to what is known in J ...
student organisations. He also helped to manage the university's cooperative bookstore, where he met and in 1972 married another bookstore manager, Joy FitzRoy. On finishing his studies in 1969, van der Poorten joined the UNSW faculty as a lecturer in pure mathematics. He became senior lecturer in 1972 and associate professor in 1976. In 1979 he moved to Macquarie University to become full professor and head of the School of Mathematics, Physics, Computing and Electronics, an administrative role that he served until 1987 and then resumed from 1991 to 1996. From 1991 onwards he also directed the Centre for Number Theory Research at Macquarie. He retired in 2002. In 1973, van der Poorten founded the ''Australian Mathematical Society Gazette'', and he continued to edit it until 1977. He was elected president of the
Australian Mathematical Society The Australian Mathematical Society (AustMS) was founded in 1956 and is the national society of the mathematics profession in Australia. One of the Society's listed purposes is to promote the cause of mathematics in the community by representing ...
in 1996. Van der Poorten was also active in
science fiction fandom Science fiction fandom or SF fandom is a community or fandom of people interested in science fiction in contact with one another based upon that interest. SF fandom has a life of its own, but not much in the way of formal organization (although ...
, beginning in the mid-1960s. He was an early member of the Sydney Science Fiction Foundation, attended the first SynCon in 1970, became friends with ''
Locus Locus (plural loci) is Latin for "place". It may refer to: Entertainment * Locus (comics), a Marvel Comics mutant villainess, a member of the Mutant Liberation Front * ''Locus'' (magazine), science fiction and fantasy magazine ** ''Locus Award ...
'' publisher
Charles N. Brown Charles Nikki Brown (June 24, 1937 – July 12, 2009) was an American publishing editor, the co-founder and editor of ''Locus'', the long-running news and reviews magazine covering the genres of science fiction and fantasy literature. Brown was bo ...
and (with psychologist Tom Newlyn) was known as one of "Sydney's terrible twins". His fannish activities significantly lessened by the late 1970s, but as late as 1999 he was a member of the 57th World Science Fiction Convention in Sydney where he helped operate the ''Locus'' table.


Research

Van der Poorten was the author of approximately 180 publications in number theory, on subjects that included
Baker's theorem In transcendental number theory, a mathematical discipline, Baker's theorem gives a lower bound for the absolute value of linear combinations of logarithms of algebraic numbers. The result, proved by , subsumed many earlier results in transcendenta ...
,
continued fraction In mathematics, a continued fraction is an expression obtained through an iterative process of representing a number as the sum of its integer part and the reciprocal of another number, then writing this other number as the sum of its integ ...
s,
elliptic curve In mathematics, an elliptic curve is a smooth, projective, algebraic curve of genus one, on which there is a specified point . An elliptic curve is defined over a field and describes points in , the Cartesian product of with itself. If ...
s,
regular language In theoretical computer science and formal language theory, a regular language (also called a rational language) is a formal language that can be defined by a regular expression, in the strict sense in theoretical computer science (as opposed to ...
s, the
integer sequence In mathematics, an integer sequence is a sequence (i.e., an ordered list) of integers. An integer sequence may be specified ''explicitly'' by giving a formula for its ''n''th term, or ''implicitly'' by giving a relationship between its terms. Fo ...
s derived from
recurrence relation In mathematics, a recurrence relation is an equation according to which the nth term of a sequence of numbers is equal to some combination of the previous terms. Often, only k previous terms of the sequence appear in the equation, for a paramete ...
s, and
transcendental number In mathematics, a transcendental number is a number that is not algebraic—that is, not the root of a non-zero polynomial of finite degree with rational coefficients. The best known transcendental numbers are and . Though only a few classe ...
s. Some of his significant results include the 1988 solution of Pisot's conjecture on the rationality of Hadamard quotients of
rational functions In mathematics, a rational function is any function that can be defined by a rational fraction, which is an algebraic fraction such that both the numerator and the denominator are polynomials. The coefficients of the polynomials need not be r ...
, his 1992 work with
Bernard Dwork Bernard Morris Dwork (May 27, 1923 – May 9, 1998) was an American mathematician, known for his application of ''p''-adic analysis to local zeta functions, and in particular for a proof of the first part of the Weil conjectures: the rationality ...
on the Eisenstein constant, his work with
Enrico Bombieri Enrico Bombieri (born 26 November 1940, Milan) is an Italian mathematician, known for his work in analytic number theory, Diophantine geometry, complex analysis, and group theory. Bombieri is currently Professor Emeritus in the School of Mathe ...
on
Diophantine approximation In number theory, the study of Diophantine approximation deals with the approximation of real numbers by rational numbers. It is named after Diophantus of Alexandria. The first problem was to know how well a real number can be approximated by ...
of
algebraic number An algebraic number is a number that is a root of a non-zero polynomial in one variable with integer (or, equivalently, rational) coefficients. For example, the golden ratio, (1 + \sqrt)/2, is an algebraic number, because it is a root of the p ...
s, and his 1999 paper with Kenneth Stuart Williams on the
Chowla–Selberg formula In mathematics, the Chowla–Selberg formula is the evaluation of a certain product of values of the gamma function at rational values in terms of values of the Dedekind eta function at imaginary quadratic irrational numbers. The result was essent ...
. He had many co-authors, the most frequent being his colleague John H. Loxton, who joined the UNSW faculty in 1972 and who later like van der Poorten moved to Macquarie. As well as publishing his own research, van der Poorten was noted for his expository writings, among them a paper on
Apéry's theorem In mathematics, Apéry's theorem is a result in number theory that states the Apéry's constant ζ(3) is irrational. That is, the number :\zeta(3) = \sum_^\infty \frac = \frac + \frac + \frac + \cdots = 1.2020569\ldots cannot be written as a fra ...
on the irrationality of ζ(3) and his book on
Fermat's Last Theorem In number theory, Fermat's Last Theorem (sometimes called Fermat's conjecture, especially in older texts) states that no three positive integers , , and satisfy the equation for any integer value of greater than 2. The cases and have bee ...
.


Awards and honours

Van der Poorten received the Australian Youth Citizenship Award in 1966 for his student leadership activities. He became a member of the
Order of Australia The Order of Australia is an honour that recognises Australian citizens and other persons for outstanding achievement and service. It was established on 14 February 1975 by Elizabeth II, Queen of Australia, on the advice of the Australian Go ...
in 2004. With Ian Sloan, van der Poorten was awarded one of two of the inaugural George Szekeres Medals of the
Australian Mathematical Society The Australian Mathematical Society (AustMS) was founded in 1956 and is the national society of the mathematics profession in Australia. One of the Society's listed purposes is to promote the cause of mathematics in the community by representing ...
in 2002, and he became an honorary member of the society in 2009.


Selected publications

* . * . * . Corrected in ''Duke Math. J.'' 76 (2): 669–672, 1994, . * . * . Corrected in ''Can. J. Math.'' 53 (2): 434–438, 2001, . *Co-authore
Recurrence Sequences
with
Graham Everest Graham Robert Everest (14 December 1957 in Southwick, West Sussex – 30 July 2010) was a British mathematician working on arithmetic dynamics and recursive equations in number theory. Life Everest studied at Bedford College (now Royal Hollo ...
, Thomas Ward, and Igor Shparlinski: American Math. Society (2003)


References

{{DEFAULTSORT:Van der Poorten, Alfred Jacobus 1942 births 2010 deaths Number theorists Fermat's Last Theorem Members of the Order of Australia Poorten, Alfred van der University of New South Wales alumni University of New South Wales faculty Macquarie University faculty Poorten, Alfred van der Australian people of Dutch-Jewish descent Australian Zionists People educated at Sydney Boys High School 20th-century Australian mathematicians 21st-century Australian mathematicians