My friend Nelson Stephens died peacefully, with family members at his side, on 8 January 2024. He had a wonderful sense of humour and he would have enjoyed the ambiguity in the previous sentence. That humorous side of him was evident on many occasions: as limerick writer on the blackboard in the Mathematics common room in Cardiff, in his gentle takedowns of self-important colleagues, in his ability to find absurdity in the most prosaic of situations, and in his delighted grin when he managed to lull you into an error. All benign, none malign.
I met Nelson in 1972 when he joined the department of Computing Mathematics at University College, Cardiff. I warmed to him immediately and for 10 years we were close friends, played badminton and Othello together, enjoyed our families meeting for dinner, and we went on many outings together. I particularly remember the occasion when Fred Lunnon led a walk to the Waterfall Country around Ystradfellte in the Neath Valley. We had to make a number of tricky river-crossings that Nelson struggled cheerfully with (he had a life-long foot problem that must have affected his balance).
The department specialised in using computers to solve problems in Pure Mathematics. This was Nelson's forte and he had already done significant work both in his PhD studies and at the Atlas Computing Laboratory in Number Theory where he was an expert in elliptic curves. This esoteric subject eventually became very important in cryptography and Nelson remained an active researcher in the field throughout his academic career. Luckily for me his expertise and interests were much wider than that and I knew I was fortunate to have a colleague that I could discuss mathematics with.
In 1975 I attended a series of lectures he gave to our Masters students, largely working through some of the chapters of Hopcroft and Ullman's new book which became very influential in the young field of data structures and algorithms. I learnt a great deal from these lectures and particularly enjoyed the lectures on the Finite Fourier Transform and Matrix Multiplication. Nelson and I began to think about the general context for these two topics: the computation of several bilinear forms. This this led to our publishing two papers that are still being cited. I remember how this research was kick-started. Nelson met me in the department one morning excited by an idea he'd had in bed: it involved solving a generalised eigenvalue equation and we both knew it was a breakthrough.
I left Cardiff in 1982 but we remained very close friends with me visiting him several times over the years. Whenever we met we slipped back into an easy familiarity sharing our personal pleasures and problems. On one of my visits he took me to his bridge club in Cardiff. I was nothing like as good a player as him but that evening we had a very good game together topping the field and winning about £40.
We never published together again although there was one year when I managed to interest him in an algebraic problem. In a very short time he produced a computer program that generated a large amount of useful data that we pored over together making various conjectures. Nelson then applied for and received a small grant from the UK Engineering and Physical Science Research Council to enable us to visit one another. Unfortunately this never came to fruition because I emigrated to New Zealand.
Nelson left Cardiff after about 20 years to become Professor of Computing at Goldsmiths College, London. He did not give up his home in Cardiff and undertook the challenging London-Cardiff commute. On the only occasion I visited him at Goldsmiths I had the impression that he was coping with the new challenges there but it was very hard work.
Throughout his life Nelson took a keen interest in politics. He was a staunch member of the Labour party and I can attribute my own passage from the political centre to the political left partly to him. I remember once joking with him that the Labour party was his natural home as he shared his birthday with Tony Blair.
One of the things I particularly admired in him was his personal modesty. We both deplored that new breed of academic who have unbounded egos. Nelson was not like that. He spoke frankly when it was warranted but never rudely. He listened attentively rather than switching off and using the time you were speaking to prepare his next statement about himself. As a result conversation with him was a delight.
Farewell, my good friend. You leave me with a treasure trove of wonderful memories.
