March 1971 - Vol. 14 No. 3

A television-like scanned-display system has been successfully implemented on a Honeywell DDP-224 computer installation. The scanned image is stored in the core memory of the computer, and software scan conversion is used to convert the rectangular coordinates of a point to the appropriate word and bit in an output display array in core storage. Results thus far indicate that flicker-free displays of large amounts of data are possible with reasonably fast graphical interaction. A scanned image of size 240 X 254 points is displayed at a 30 frame-per-second rate.

An elementary outline of the theorem-proving approach to automatic program synthesis is given, without dwelling on technical details. The method is illustrated by the automatic construction of both recursive and iterative programs operating on natural numbers, lists, and trees. In order to construct a program satisfying certain specifications, a theorem induced by those specifications is proved, and the desired program is extracted from the proof. The same technique is applied to transform recursively defined functions into iterative programs, frequently with a major gain in efficiency. It is emphasized that in order to construct a program with loops or with recursion, the principle of mathematical induction must be applied. The relation between the version of the induction rule used and the form of the program constructed is explored in some detail.

This paper presents the scheduling algorithm used in the Computer Assisted Registration System at the University of Tennessee. Notation is defined and the logic of the algorithm necessary to implement educational policy is described. Results from the first term's implementation are presented.

The utilization of storage is studied in a two-level memory hierarchy. The first storage level, which is the fast store, is divided into a number of storage areas. When an entry is to be filed in the hierarchy, a hashing algorithm will attempt to place the entry into one of these areas. If this particular area is full, then the entry will be placed into the slower second-level store, even though other areas in the first-level store may have space available. Given that N entries have been filed in the entire hierarchy, an expression is derived for the expected number of entries filed in the first-level store. This expression gives a measure of how effectively the first-level store is being used. By means of examples, storage utilization is then studied as a function of the hashing algorithm, the number of storage areas into which the first-level store is divided and the total size of the first-level store.

An integration technique for the automatic solution of an initial value problem for a set of ordinary differential equations is described. A criterion for the selection of the order of approximation is proposed. The objective of the criterion is to increase the step size so as to reduce solution time. An option permits the solution of “stiff” differential equations. A program embodying the techniques discussed appears in Algorithm 407.