Jean Delsarte

Jean Frédéric Auguste Delsarte (born October 19, 1903 in Fourmies , † November 28, 1968 in Nancy ) was a French mathematician who was one of the founders of Bourbaki .

Delsarte's father ran a textile factory in Fourmies, which was captured by the Germans in 1914 during the First World War. Delsarte therefore went on to school in Rouen, where he received a medal for his academic achievements in 1920. From 1922 he studied at the École normal supérieure . There he met fellow students like André Weil and Henri Cartan , with whom he was to found Bourbaki in 1935. In 1925 he completed his studies and after his military service worked on a grant from the Thiers Foundation on his doctoral thesis Les rotations fonctionnelles , with which he received his doctorate in 1928.

In the same year (1928) he went to Nancy University , where he stayed for the rest of his career. In 1932 he gave a lecture at the International Congress of Mathematicians in Zurich. In Nancy he held lectures in mathematics (for example, on linear transformations in Hilbert spaces and differential equations, as well as lectures on relativity theory) and public courses on astronomy. He also read at the Collège de France in Paris in 1931 and later at the Institut Henri Poincaré . At a meeting with his Parisian friends in Paris in 1934/35 the idea for a new analysis textbook arose, which then became the Bourbaki project. In 1936 he became a professor of higher analysis in Nancy. With Weil and Cartan, who were in Strasbourg at the time, he organized a joint seminar and brought Jean Leray to Nancy, who became professor of applied mathematics there in 1938. In the same year Jean Dieudonné came to Nancy. At the same time he was organizationally active, for example as scientific director at the CNRS from 1932 to 1936 and in the admission commissions and examination commissions of schools (1928/29 even in Poland).

During the Second World War he initially served as an artillery officer and returned to the University of Nancy during the occupation, where he became faculty chairman in 1944 and dean from 1945 to 1948. Even after the war he brought outstanding mathematicians to Nancy such as Laurent Schwartz , Roger Godement , Jean-Pierre Serre and Jacques-Louis Lions and founded the Elie Cartan Institute in Nancy based on the model of the Paris Poincaré Institute. In addition, he was visiting professor at numerous universities abroad, including 1947 at the Institute for Advanced Study and regularly from 1948 to 1951 in São Paulo , but also in India, Canada, Mexico, China, Japan and the Soviet Union. He died of a heart attack in 1968.

Delsarte was an analyst who, among other things, dealt with near-periodic functions , series developments of functions and harmonic functions . He extended Gauss's theorem that a function whose function value is equal to the mean value of the function at any point on spheres of any radius is harmonic. According to Delsarte, it is sufficient if its function value is equal to the mean value on two radii, if the radius ratios do not assume a finite number of specific values. ${\displaystyle f}$ ${\displaystyle x}$ ${\displaystyle x}$

He had been married since 1929 and had two daughters.

In 1954 he was knight of the Legion of Honor and in 1962 commander of the Palmes Académique. In 1964 he received the Bordin Prize from the French Academy of Sciences.

Web links

• John J. O'Connor, Edmund F. Robertson :  Jean Delsarte. In: MacTutor History of Mathematics archive .