Kenneth E. Iverson

Life

Ken Iverson was born on 17 December 1920 near Camrose, a town in central Alberta, Canada. His parents were farmers who came to Alberta from North Dakota; his ancestors came from Trondheim, Norway.

During World War II, he served first in the Canadian Army and then in the Royal Canadian Air Force. He received a B.A. degree from Queen's University and the M.Sc. and Ph.D. degrees from Harvard University. In his career, he worked for Harvard, IBM, I. P. Sharp Associates, and Jsoftware Inc. (née Iverson Software Inc.).

Iverson suffered a stroke while working at the computer on a new J lab on 16 October 2004, and died in Toronto on 19 October 2004 at age 83.

Education

Iverson began school on 1 April 1926 in a one-room school, initially in Grade 1, promoted to Grade 2 after 3 months and to Grade 4 by the end of June 1927.

He left school after Grade 9 because it was the depths of the Great Depression and there was work to do on the family farm, and because he thought further schooling only led to becoming a schoolteacher and he had no desire to become one. At age 17, while still out of school, he enrolled in a correspondence course on radios with De Forest Training in Chicago, and learned calculus by self-study from a textbook.

During World War II, while serving in the Royal Canadian Air Force, he took correspondence courses toward a high school diploma.

After the war, Iverson enrolled in Queen's University in Kingston, Ontario, taking advantage of government support for ex-servicemen and under threat from an Air Force buddy who said he would "beat his brains out if he did not grasp the opportunity". He graduated in 1950 as the top student with a bachelor's degree in mathematics and physics.

Continuing his education at Harvard University, he began in the Department of Mathematics and received a master's degree in 1951. He then switched to the Department of Engineering and Applied Physics, working with Howard Aiken and Wassily Leontief.

Kenneth Iverson has recalled graduate study under Aiken as "like an apprenticeship" in which the student "learned the tools of the scholarship trade". Every topic was "used more as a focus for the development of skills such as clarity of thought and expression than as an end in itself". Once admitted to the program, a graduate student underwent a rite of "adoption into the fold". He was given a desk (or a share of a desk) among a group of other graduate students, the permanent staff, or visiting scholars, "most of whom were engaged in some aspect of the design and building of computers". A student was thus "made to feel part of a scholarly enterprise" and was provided, "often for the first time, with easy and intimate access to others more experienced in his chosen field".

When interviewing Aiken, I had asked him whether Tropp and I might see his lecture notes; Aiken replied that he had always destroyed his lecture notes at the end of each year, so that he would not be tempted to repeat his lectures.

Work

Harvard (1955–1960)

Iverson stayed on at Harvard as an assistant professor to implement the world's first graduate program in "automatic data processing".

Many people think that Aiken was interested only in scientific computers. This was simply not so. During one coffee hour, Aiken turned to Ken Iverson, who had just finished his Ph.D., and said: "These machines are going to be immensely important for business, and I want you to prepare and teach a course in business data processing next fall." There had never been such a course anywhere in the world. Ken was qualified only because he was a mathematician. I was so excited by the prospect that I immediately volunteered to be Ken's graduate teaching assistant.

It was in this period that Iverson developed notation for describing and analyzing various topics in data processing, for teaching classes, and for writing (with Brooks) Automatic Data Processing. He was "appalled" to find that conventional mathematical notation failed to fill his needs, and began work on extensions to the notation that were more suitable. In particular, he adopted the matrix algebra used in his thesis work, the systematic use of matrices and higher-dimensional arrays in tensor analysis, and operators in the sense of Heaviside in his treatment of Maxwell's equations, higher-order functions on function argument(s) with a function result. The notation was also field-tested in the business world in 1957 during a 6-month sabbatical spent at McKinsey & Company. The first published paper using the notation was The Description of Finite Sequential Processes, initially Report Number 23 to Bell Labs and later revised and presented at the Fourth London Symposium on Information Theory in August 1960.

Iverson stayed at Harvard for five years but failed to get tenure, because "[he hadn't] published anything but the one little book".

IBM (1960–1980)

Iverson joined IBM Research in 1960 (and doubled his salary). He was preceded to IBM by Fred Brooks, who advised him to "stick to whatever [he] really wanted to do, because management was so starved for ideas that anything not clearly crazy would find support." In particular, he was allowed to finish and publish A Programming Language and (with Brooks) Automatic Data Processing, two books that described and used the notation developed at Harvard. (Automatic Data Processing and A Programming Language began as one book "but the material grew in both magnitude and level until a separation proved wise".)

At IBM, Iverson soon met Adin Falkoff, and they worked together for the next twenty years. Chapter 2 of A Programming Language used Iverson's notation to describe the IBM 7090 computer. In early 1963 Falkoff, later joined by Iverson and Ed Sussenguth, proceeded to use the notation to produce a formal description of the IBM System/360 computer then under design. The result was published in 1964 in a double issue of the IBM Systems Journal, thereafter known as the "grey book" or "grey manual". The book was used in a course on computer systems design at the IBM Systems Research Institute. A consequence of the formal description was that it attracted the interest of bright young minds. One hotbed of interest was at Stanford University which included Larry Breed, Phil Abrams, Roger Moore, Charles Brenner, and Mike Jenkins, all of whom later made contributions to APL. Donald McIntyre, head of geology at Pomona College which had the first general customer installation of a 360 system, used the formal description to become more expert than the IBM systems engineer assigned to Pomona.

With the completion of the formal description Falkoff and Iverson turned their attention to implementation. This work was brought to rapid fruition in 1965 when Larry Breed and Phil Abrams joined the project. They produced a FORTRAN-based implementation on the 7090 called IVSYS (for Iverson system) by autumn 1965, first in batch mode and later, in early 1966, in time-shared interactive mode. Subsequently, Breed, Dick Lathwell (ex University of Alberta), and Roger Moore (of I. P. Sharp Associates) produced the System/360 implementation; the three received the Grace Murray Hopper Award in 1973 "for their work in the design and implementation of APL\360, setting new standards in simplicity, efficiency, reliability and response time for interactive systems." While the 360 implementation work was underway "Iverson notation" was renamed "APL", by Falkoff. The workspace "1 cleanspace" was saved at 1966-11-27 22.53.58 UTC. APL\360 service began within IBM several weeks before that and outside IBM in 1968. Additional information on the implementation of APL\360 can be found in the Acknowledgements of the APL\360 User's Manual and in "Appendix. Chronology of APL development" of The Design of APL.

I. P. Sharp Associates (1980–1987)

In 1980, Iverson left IBM for I. P. Sharp Associates, an APL time-sharing company. He was preceded there by his IBM colleagues Paul Berry, Joey Tuttle, Dick Lathwell, and Eugene McDonnell. At IPSA, the APL language and systems group was managed by Eric Iverson (Ken Iverson's son); Roger Moore, one of the APL\360 implementers, was a vice president.

Iverson worked to develop and extend APL on the lines presented in Operators and Functions. The language work gained impetus in 1981 when Arthur Whitney and Iverson produced a model of APL written in APL at the same time they were working on IPSA's OAG database. (Iverson introduced Arthur Whitney, son of Eoin Whitney, to APL when he was 11 years old and in 1974 recommended him for a summer student position at IPSA Calgary.) In the model, the APL syntax was driven by an 11-by-5 table. Whitney also invented the rank operator in the process. The language design was further simplified and extended in Rationalized APL in January 1983, multiple editions of A Dictionary of the APL Language between 1984 and 1987, and A Dictionary of APL in September 1987. Within IPSA, the phrase "dictionary APL" came into use to denote the APL specified by A Dictionary of APL, itself referred to as "the dictionary". In the dictionary, APL syntax is controlled by a 9-by-6 table and the parsing process was precisely and succinctly described in Table 2, and there is a primitive (monadic ⊥, modeled in APL) for word formation (lexing).

In the 1970s and 1980s, the main APL vendors were IBM, STSC, and IPSA, and all three were active in developing and extending the language. IBM had APL2, based on the work of Jim Brown. Work on APL2 proceeded intermittently for 15 years, with actual coding starting in 1971 and APL2 becoming available as an IUP (Installed User Program, an IBM product classification) in 1982. STSC had an experimental APL system called NARS, designed and implemented by Bob Smith. NARS and APL2 differed in fundamental respects from dictionary APL, and differed from each other.

I.P. Sharp implemented the new APL ideas in stages: complex numbers, enclosed (boxed) arrays, match, and composition operators in 1981, the determinant operator in 1982, and the rank operator, link, and the left and right identity functions in 1983. However, the domains of operators were still restricted to the primitive functions or subsets thereof. In 1986, IPSA developed SAX, SHARP APL/Unix, written in C and based on an implementation by STSC. The language was as specified in the dictionary with no restrictions on the domains of operators. An alpha version of SAX became available within I.P. Sharp around December 1986 or early 1987.

Jsoftware (1990–2004)

Iverson retired from I. P. Sharp Associates in 1987. He kept busy while "between jobs". Regarding language design, the most significant of his activities in this period was the invention of "fork" in 1988. For years, he had struggled to find a way to write f+g as in calculus, from the "scalar operators" in 1978, through the "til" operator in 1982, the catenation and reshape operators in 1984, the union and intersection operators in 1987, "yoke" in 1988, and finally forks in 1988. Forks are defined as follows:

Moreover, (f g p q r) ←→ (f g (p q r)). Thus to write f+g as in calculus, one can write f+g in APL. Iverson and Eugene McDonnell worked out the details on the long plane rides to the APL88 conference in Sydney, Australia, with Iverson coming up with the initial idea on waking up from a nap.

Iverson presented the rationale for his work post 1987 as follows:

When I retired from paid employment, I turned my attention back to this matter [the use of APL for teaching] and soon concluded that the essential tool required was a dialect of APL that:

• Is available as "shareware", and is inexpensive enough to be acquired by students as well as by schools

• Can be printed on standard printers

• Runs on a wide variety of computers

• Provides the simplicity and the generality of the latest thinking in APL

The result has been J, first reported in [the APL 90 Conference Proceedings].

Roger Hui described the final impetus that got J started in Appendix A of An Implementation of J:

One summer weekend in 1989, Arthur Whitney visited Ken Iverson at Kiln Farm and produced—on one page and in one afternoon—an interpreter fragment on the AT&T 3B1 computer. I studied this interpreter for about a week for its organization and programming style; and on Sunday, August 27, 1989, at about four o'clock in the afternoon, wrote the first line of code that became the implementation described in this document.

Awards and honors

IBM Fellow, IBM, 1970

Harry H. Goode Memorial Award, IEEE Computer Society, 1975

Member, National Academy of Engineering (USA), 1979

Turing Award, Association for Computing Machinery, 1979

Computer Pioneer Award (Charter recipient), IEEE Computer Society, 1982

Honorary doctorate, York University, 1998

In 2015, a new moth species, Agdistis iversoni, was named after him.