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 algebra ...
, the Phragmén–Lindelöf principle (or method), first formulated by
Lars Edvard Phragmén
Lars Edvard Phragmén (2 September 1863 Örebro – 13 March 1937) was a Swedish mathematician.
The son of a college professor, he studied at Uppsala then Stockholm, graduating from Uppsala in 1889. He became professor at Stockholm in 1892, aft ...
(1863–1937) and
Ernst Leonard Lindelöf
Ernst Leonard Lindelöf (; 7 March 1870 – 4 June 1946) was a Finnish mathematician, who made contributions in real analysis, complex analysis and topology. Lindelöf spaces are named after him. He was the son of mathematician Lorenz Leonard ...
(1870–1946) in 1908, is a technique which employs an auxiliary, parameterized function to prove the boundedness of a holomorphic function
(i.e,