James Anthony Dominic Welsh (known professionally as D.J.A. Welsh, 29 August 1938 – 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.
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]
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.