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

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, mathematical structure, structure, space, Mathematica ...

and

engineer Engineers, as practitioners of engineering, are professionals who Invention, invent, design, build, maintain and test machines, complex systems, structures, gadgets and materials. They aim to fulfill functional objectives and requirements while ...

. He was the president of the Danish Mathematical Society from 1892 to 1903.

Biography

Jensen was born in

Nakskov Nakskov is a market town on the island of Lolland in south Denmark. The town has a population of 12,200 (1 January 2025) and is the largest town on the island of Lolland. It is located in Lolland municipality in Region Sjælland. Nakskov is situ ...

Denmark Denmark is a Nordic countries, Nordic country in Northern Europe. It is the metropole and most populous constituent of the Kingdom of Denmark,, . also known as the Danish Realm, a constitutionally unitary state that includes the Autonomous a ...

, 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 maths topics later by himself and never held any

academic An academy (Attic Greek: Ἀκαδήμεια; Koine Greek Ἀκαδημία) is an institution of tertiary education. The name traces back to Plato's school of philosophy, founded approximately 386 BC at Akademia, a sanctuary of Athena, the go ...

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: * Inequality (mathematics), a relation between two quantities when they are different. * Economic inequality, difference in economic well-being between population groups ** Income inequality, an unequal distribution of i ...

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 p ...

. In 1915, Jensen also proved Jensen's formula in

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

References

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

Biography

See also

References