OBITUARIES: PROFESSOR BILL PARRY ; 11-Plus-Failure Mathematician FRS
Walters, Peter, The Independent (London, England)
Bill Parry had a meagre school education but went on be an outstanding mathematician in the field of dynamical systems and a Fellow of the Royal Society. He specialised in ergodic theory, which has close connections with probability theory, statistical mechanics, number theory, differential equations and information theory.
Parry was born in Coventry in 1934, the sixth of a family of seven children. He failed his 11-plus examination and at the age of 13 went to a technical school which specialised in woodwork and metalwork but where a teacher noticed his mathematical ability and persuaded him to stay in the sixth form. Because the school was unable to provide proper tuition in mathematics, Parry was obliged to take classes at Birmingham Technical College, and, after obtaining the requisite passes, he was, despite the limitations of his schooling, admitted to University College London to study Mathematics, where he was encouraged by Hyman Kestelman.
After graduating in 1955 he did a one-year MSc course at Liverpool University before studying for his doctorate at Imperial College, London, under the guidance of Yael Dowk-er. His first post was as a Lecturer in the Mathematics Department at Birmingham University.
The academic year 1962-63, spent at Yale University, was very important in Parry's mathematical development because he had close contact with Shizuo Kakutani and several young American mathematicians who were working in the same area. He returned to Birmingham with an enhanced enthusiasm for mathematics and began to supervise research students.
Parry's early research work was in several areas of ergodic theory that turned out to be of major importance. He was the first to study topological Markov chains, later called subshifts of finite type, and these became significant in some coding theory problems and as models for parts of smooth dynamical systems with hyperbolic behaviour. He showed that each irreducible topological Markov chain has a unique measure of maximal entropy and these measures, which are now called Parry measures, can be described in a simple way using matrix theory.
In 1965 he moved to the newly founded Sussex University as Senior Lecturer. There he worked on entropy theory showing, amongst other things, that each aperiodic measure-preserving transformation could be viewed as the shift on the realisation space of a stationary, countable state, stochastic process indexed by the integers or the natural numbers. He moved to Warwick University, in his home city of Coventry, in the spring of 1968 and spent the remainder of his career there.
Warwick had been founded at much the same time as Sussex and had a thriving research environment through its Mathematical Research Centre, and Parry, who previously had disliked the pretensions of common rooms, was at home in the atmosphere of discussions, both mathematical and general, in the large comfortable space adorned with many large blackboards in the Mathematics Institute.
Among his contributions during these years was fundamental work on codings between symbolic systems. Sometimes the efficiency of a code is very important. …