Sussman is a coauthor (with
Hal Abelson and
Julie Sussman) of the introductory computer science textbook used at MIT. This textbook,
Structure and Interpretation of Computer Programs, has been translated into several languages.
Sussman's contributions to
artificial intelligence include problem solving by debugging almost-right plans, propagation of constraints applied to electrical circuit analysis and synthesis, dependency-based explanation and dependency-based backtracking, and various language structures for expressing problem-solving strategies. Sussman and his former student,
Guy L. Steele Jr., invented the
Scheme programming language in
1975.
Sussman saw that artificial intelligence ideas can be applied to
computer-aided design. Sussman developed, with his graduate students, sophisticated computer-aided design tools for
VLSI. Steele made the first Scheme chips in
1978. These ideas and the AI-based CAD technology to support them were further developed in the Scheme chips of
1979 and
1981. The technique and experience developed was then used to design other special-purpose computers. Sussman was the principal designer of the
Digital Orrery, a machine designed to do high-precision integrations for
orbital mechanics experiments. The Orrery was designed and built by a few people in a few months, using AI-based simulation and compilation tools.
Using the Digital Orrery, Sussman has worked with
Jack Wisdom to discover numerical evidence for chaotic motions in the outer planets. The Digital Orrery is now retired at the
Smithsonian Institution in Washington, DC. Sussman was also the lead designer of the Supercomputer Toolkit, another
multiprocessor computer optimized for evolving systems of
ordinary differential equations. The Supercomputer Toolkit was used by Sussman and Wisdom to confirm and extend the discoveries made with the Digital Orrery to include the entire planetary system.
Sussman has pioneered the use of computational descriptions to communicate methodological ideas in teaching subjects in Electrical Circuits and in Signals and Systems. Over the past decade Sussman and Wisdom have developed a subject that uses computational techniques to communicate a deeper understanding of advanced
classical mechanics. In
Computer Science: Reflections on the Field, Reflections from the Field, he writes "...computational algorithms are used to express the methods used in the analysis of dynamical phenomena. Expressing the methods in a computer language forces them to be unambiguous and computationally effective. Students are expected to read the programs and to extend them and to write new ones. The task of formulating a method as a computer-executable program and debugging that program is a powerful exercise in the learning process. Also, once formalized procedurally, a mathematical idea becomes a tool that can be used directly to compute results." Sussman and Wisdom, with Meinhard Mayer, have produced a textbook,
Structure and Interpretation of Classical Mechanics, to capture these new ideas.
Sussman and Abelson also have been an important part of the
Free Software Movement, including serving on the Board of Directors of the
Free Software Foundation,http://www.fsf.org/about/leadership.html and releasing
MIT/GNU Scheme as
free software even before the Free Software Foundation existed.
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