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 Lindelöf, whose chair he would eventually succeed through his cousin , and brother of the philologist . He founded the Finnish school of function theory, which achieved lasting international renown.
He was secretary of the Finnish Society of Science and Letters (societas scientiarum Fennica) in its centenary year, 1938.
Biography
Early life and education
Lindelöf was born in Helsingfors into a mathematical family: his father Lorenz Leonard Lindelöf was professor of mathematics at the University of Helsinki, and just over a decade later that same chair passed to his cousin . When Lindelöf succeeded his cousin at the age of 33, he completed a remarkable mathematical dynasty spanning three generations of the same family.
Lindelöf showed an early talent for mathematics and decided as a schoolboy to follow his father's path. He retired in 1938.
After the turn of the century, Lindelöf made two extended visits to Göttingen. His period of active research lasted roughly until 1915. He is known for the Picard–Lindelöf theorem on differential equations and the Phragmén–Lindelöf principle, one of several refinements of the maximum modulus principle that he proved in complex function theory, the latter developed in collaboration with Lars Edvard Phragmén.
Music was a lifelong interest. As a violinist he far exceeded ordinary amateur level. As a student he played in a quartet that also included Jean Sibelius. He later served on the board of the Helsinki Philharmonic Orchestra. He received honorary doctorates from the universities of Oslo (1929), Uppsala (1932), and Stockholm (1936).