Joseph D. Rutledge

On Ianov's Program Schemata

Ianov has defined a formal abstraction of the notion of program which represents the sequential and control properties of a program but suppresses the details of the operations. For these schemata he defines a notion corresponding to computation and defines equivalence of schemata in terms of it. He then gives a decision procedure for equivalence of schemata, and a deductive formalism for generating schemata equivalent to a given one. The present paper is intended, first as an exposition of Ianovs results and simplification of his method, and second to point out certain generalizations and extensions of it. We define a somewhat generalized version of the notion of schema, in a language similar to that used in finite automata theory, and present a simple algorithm for the equivalence problem solved by Ianov. We also point out that the same problem for an extended notion of schema, considered rather briefly by Ianov, is just the equivalence problem for finite automata, which has been solved, although the decision procedure is rather long for practical use. A simple procedure for generating all schemata equivalent to a given schema is also indicated.

Negative inertia: a dynamic pointing function

In-keyboard isometric joysticks can give better performance than mice for mixed typing/pointing tasks. The continuing challenge is to improve such devices to the point that they are preferable even for pure pointing tasks. Previous work has improved joystick performance by considering user perception and motor skills. This paper considers the dynamics of the pointing operation. A dynamic transfer function for an isometric joystick is described which amplifies changes in the applied force to increase responsiveness without loss of control. User tests show a 7.8 +/3.5% performance improvement over a standard non-dynamic joystick. This feature has been incorporated into the TrackPoint III from IBM.

Scalar and vector iteration

In “Monadic Computation and Iterative Algebraic Theories” Elgot [3] introduced the notion of a vector iterative theory and showed that vector iterative theories have a close connection with several aspects of the theory of computation. In private conversations Elgot formulated the notion of a scalar iterative theory and raised the question whether scalar and vector iterative theories coincide. We answer this question in the affirmative.