Johan Ludwig William Valdemar Jensen, mostly known as Johan Jensen (8 May 1859 – 5 March 1925), was a

Danish Danish may refer to: * Something of, from, or related to the country of Denmark People * A national or citizen of Denmark, also called a "Dane," see Demographics of Denmark * Culture of Denmark * Danish people or Danes, people with a Danish ance ...

mathematician A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems. Mathematicians are concerned with numbers, data, quantity, structure, space, models, and change. History On ...

and

engineer Engineers, as practitioners of engineering, are professionals who invent, design, analyze, build and test machines, complex systems, structures, gadgets and materials to fulfill functional objectives and requirements while considering the l ...

. He was the president of the

Danish Mathematical Society The Danish Mathematical Society (Dansk Matematisk Forening) is a society of Denmark, Danish mathematicians founded in 1873 at the University of Copenhagen, a year after the Société Mathématique de France, French Mathematical Society. According t ...

from 1892 to 1903.

Biography

Jensen was born in

Nakskov Nakskov is a town in south Denmark. It is situated in Lolland municipality in Region Sjælland on the western coast of the island of Lolland. The town has a population of 12,495 (1 January 2022). To the west is Nakskov Fjord, an inlet from the La ...

Denmark ) , song = ( en, "King Christian stood by the lofty mast") , song_type = National and royal anthem , image_map = EU-Denmark.svg , map_caption = , subdivision_type = Sovereign state , subdivision_name = Danish Realm, Kingdom of Denmark ...

, but spent much of his childhood in northern Sweden, because his father obtained a job there as the manager of an estate. Their family returned to Denmark before 1876, when Jensen enrolled to the College of Advanced Technology. Although he studied mathematics among various subjects at college, and even published a research paper in mathematics, he learned advanced math topics later by himself and never held any

academic An academy (Attic Greek: Ἀκαδήμεια; Koine Greek Ἀκαδημία) is an institution of secondary education, secondary or tertiary education, tertiary higher education, higher learning (and generally also research or honorary membershi ...

position. Instead, he was a successful engineer for the Copenhagen Telephone Company between 1881 and 1924, and became head of the technical department in 1890. All his mathematics research was carried out in his spare time. Jensen is mostly renowned for his famous

inequality Inequality may refer to: Economics * Attention inequality, unequal distribution of attention across users, groups of people, issues in etc. in attention economy * Economic inequality, difference in economic well-being between population groups * ...

Jensen's inequality In mathematics, Jensen's inequality, named after the Danish mathematician Johan Jensen, relates the value of a convex function of an integral to the integral of the convex function. It was proved by Jensen in 1906, building on an earlier pr ...

. In 1915, Jensen also proved

Jensen's formula In the mathematical field known as complex analysis, Jensen's formula, introduced by , relates the average magnitude of an analytic function on a circle with the number of its zeros inside the circle. It forms an important statement in the study ...

complex analysis Complex analysis, traditionally known as the theory of functions of a complex variable, is the branch of mathematical analysis that investigates Function (mathematics), functions of complex numbers. It is helpful in many branches of mathemati ...

References

{{DEFAULTSORT:Jensen, Johan 1859 births 1925 deaths 19th-century Danish mathematicians 20th-century Danish mathematicians Number theorists Danish engineers People from Nakskov