A GIFTED mathematician and a charismatic teacher, Ken Iverson made a highly influential contribution to the field of computer science. In the early 1960s a mathematical notation which he had developed as an aide to teaching algebra formed the basis of APL, one of the languages used in programming IBM’s early mainframe computer, the System/360. This concise and powerful language contributed substantially to IBM’s domination of the emerging computer industry during the 1960s and 1970s.

Kenneth Eugene Iverson was born in Camrose, Alberta, Canada, in 1920. He demonstrated an early aptitude for mathematics — he taught himself calculus in his teens. During the Second World War he served in the Royal Canadian Air Force as a flight engineer specialising in reconnaissance. After the war he obtained a degree in mathematics and physics from Queen’s University, Ontario, and went on to postgraduate study at Harvard where, in 1954, he obtained a doctorate in applied mathematics, and from 1955 to 1960 he was assistant professor of applied mathematics.

During this period he developed a novel way of teaching algebra to students, the “Iverson notation”. It attracted the interest of IBM, which was already well established in commercial and scientific computing fields and was developing a new mainframe, the System/360.

IBM recruited Iverson and three colleagues to turn his teaching notation into a programming language which could be used on the System/360. The result, expounded in his book A Programming Language (1962), came to be known as APL.

APL is one of the most concise, consistent and powerful programming languages yet developed. It encourages prototyping and experimentation in a way that was revolutionary at the time of its launch, and is a concrete expression of Iverson’s oft-stated view that a programming language is “a tool for thought”.

Despite its use of unusual characters, which necessitated a special keyboard, APL quickly became a popular language and was used widely in the 1960s and 1970s. Iverson continued to work on its development and implementation for many years, and was appointed an IBM Fellow in 1980 in recognition of the importance of his achievement. After leaving the company in 1980 he returned to Toronto, where he worked for IP Sharp Associates, a company that had developed System/360 programs to support time-sharing, the simultaneous use of the computer by many people.

Although he retired in 1987, Iverson remained an active researcher and worked on the development of programming languages which extended the ideas underpinning APL. The most successful of these, the J notation, has a large and growing user base in the scientific computing community. Iverson actively promoted the diffusion of J until the end of his life.

Iverson’s contribution to computer science was widely recognised. He received the Harry Goode Award in 1975, the Turing Award in 1979, the IEEE Computer Pioneer Award in 1991 and the National Medal of Technology in 1991.

Iverson was married to Jean, who survives him, along with their four children.

Kenneth Iverson, inventor of the APL programming language, was born on December 17, 1920. He died on October 19, 2004, aged 83.