Johan Frederik Steffensen

{{Short description|Danish mathematician and statistician (1873–1961)}}

Johan Frederik Steffensen (28 February 1873, in Copenhagen – 20 December 1961) was a Danish mathematician, statistician, and actuary who did research in the fields of calculus of finite differences and interpolation.{{cite journal|title=Review of (1) Interpolation Formulas, with one and more variables. Pp. 26; (2) Factorial Moments and Discontinuous Frequency Functions. Pp. 17. By J. F. Steffensen, Ph.D., [Reprinted from Skandinavisk Aktuarietidskrift. Upsala. 1923.]|journal=Journal of the Institute of Actuaries|volume=54|issue=3|year=2016|pages=301–302|issn=0020-2681|doi=10.1017/S0020268100030341|url=https://books.google.com/books?id=LA_xAAAAMAAJ&pg=PA301|url-access=subscription}} He was professor of actuarial science at the University of Copenhagen from 1923 to 1943. Steffensen's inequality and Steffensen's method (an iterative numerical method) are named after him. He was an Invited Speaker at the 1912 International Congress of Mathematicians (ICM) in Cambridge, England and at the 1924 ICM in Toronto.{{cite web|title=Steffensen, J. F.|website=ICM Plenary and Invited Speakers|url=https://www.mathunion.org/icm-plenary-and-invited-speakers?combine=Steffensen}}

{{blockquote|... His more important works included the theory of statistics (1923), interpolation (1925), insurance mathematics (1934) and the calculation of interest (1936). ... He was President of the Danish Actuarial Society in 1922-24 and 1930-33, and of the Danish Mathematical Society in 1930-36 ...{{cite journal|author=Ogborn, M. E|title=Obituary. Johan Frederik Steffensen|journal=Journal of the Institute of Actuaries|volume=88|issue=2|date=September 1962|pages=251–252|doi= 10.1017/S0020268100015067|url=https://rss.onlinelibrary.wiley.com/doi/pdfdirect/10.1111/j.2397-2327.1962.tb01021.x|doi-access=free}}}}