James Anthony Dominic Welsh (known professionally as D.J.A. Welsh) (born 29 August 1938, died 30 November 2023^[1])^[2][3] was an English mathematician and emeritus professor of Oxford University's Mathematical Institute. He was an expert in matroid theory,^[4] the computational complexity of combinatorial enumeration problems, percolation theory, and cryptography.

Biography

Welsh obtained his Doctor of Philosophy from Oxford University under the supervision of John Hammersley.^[5] After working as a researcher at Bell Laboratories, he joined the Mathematical Institute in 1963 and became a fellow of Merton College, Oxford in 1966. He chaired the British Combinatorial Committee from 1983 to 1987.^[3] Welsh was given a personal chair in 1992 and retired in 2005.^[3] He supervised 28 doctoral students.^[6]

Books

• Matroid Theory (LMS Monographs, vol. 8, Academic Press, 1976, MR0427112, reprinted by Dover Publications, 2010, ISBN 978-0486474397)
• Probability: An Introduction (with Geoffrey Grimmett, Oxford University Press, 1986, ISBN 0-19-853264-4, MR0869591)
• Codes and Cryptography (Oxford University Press, 1988, ISBN 978-0198532873, MR0959137)
• Complexity: Knots, Colourings and Counting (LMS Lecture Notes, vol. 186, Oxford University Press, 1993, ISBN 0-521-45740-8, MR1245272)
• Complexity and Cryptography: An Introduction (with John Talbot, Cambridge University Press, 2006, MR2221458)^[7]

Awards and honours

Welsh received an honorary doctorate from the University of Waterloo in 2006.^[3]

In 2007, Oxford University press published Combinatorics, Complexity, and Chance: A Tribute to Dominic Welsh, an edited volume of research papers dedicated to Welsh.^[8]

The Russo–Seymour–Welsh estimate in percolation theory is partly named after Welsh.