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Raster scan computer graphics displays with "real time" character generators have previously been limited to alphanumeric characters. A display is described which extends the capabilities of this organization to include general graphics. The feasibility of such a display is shown by deriving the minimum number of patterns required in the read only memory of the character generator to synthesize an arbitrary line. The synthesis process does not compromise picture quality, since the resulting dot patterns are identical with those of a conventional raster display. Furthermore, the time constraints of a raster display are shown to be satisfied for a typical design for very complex line drawings. [ABSTRACT FROM AUTHOR]

In radioisotope scanning, a field which is assuming increasing importance in mediccl diagnosis, the scan is a two-dimensional pattern made up of dots. Areas of increased source activity are represented on the scan by areas of increased dot density. To study the output of scanners with various characteristics, a program which simulates radioisotope scans has been written for a PDP-1 computer with auxiliary disk storage and cathode ray tube display. Past and present research using the output of the simulator has shown the flexibility of the system to be important. The structure of this program can be useful in the simulation of the output of any quantum-limited system. [ABSTRACT FROM AUTHOR]

Raster scan computer graphics with"real time" character generators have previously been limited to alphanumeric characters. A display has been described which extends the capabilities of this organization to include general graphics. Two fundamentally different scan conversion algorithms which have been developed to support this display are presented. One is most suitable to non- interactive applications and the other to Interactive applications. The algorithms were implemented in Fortran on the CDC6400 computer. Results obtained from the implementations show that the non interactive algorithms can significantly reduce display file storage requirements at little cost in execution time over that of a conventional raster display. The interactive algorithm can improve response time and reduce storage requirements. [ABSTRACT FROM AUTHOR]

Describes a scan conversion algorithm that uses a linked list data structure to process the lines of the drawing in strips corresponding to groups of scan lines. Form of display file of most graphic systems using a raster scan output device; Translation of the picture description from the XY format to the raster format; Memory buffer area used to accumulate the binary image for a group of scan lines; Line drawing analysis.

This article focuses on a newly formulated algorithm related to a minimal spanning tree clustering method, referencing a previously published article on graph-theoretical methods for detecting and describing gestalt cluster by mathematician C.T. Zahn. Zahn has described a method for automatically detecting clusters in sets of points in N-space. The method is based on the construction of the minimal spanning tree of the complete graph on the input set of points. The motivation for using the minimal spanning tree includes some evidence that it is related to human perception of dot pictures in two dimensions, but the method is applicable in any dimension. The algorithm, formulated by researcher V.K.M. Whitney, is used here which was appeared in the April 1972 issue of the journal "Communications of the ACM." The basic idea of the article's author here is to detect inherent separations in the data by deleting edges from the minimal spanning tree which are significantly longer than nearby edges.

The constructs of a simple programming language are introduced and described informally in terms of values and side-effects. A translator is defined which translates the language into flowcharts for a simple machine. The action of the machine in executing a flowchart is defined. A proof is constructed that the effect of translating and executing any program can be expressed solely in terms of the value and side-effect of the program. During the course of constructing the proof, formal definitions of the concepts of value and side-effect are derived in order to make the proof rigorous. Correctness of the implementation involves checking that the definitions derived in the step above are an acceptable formalization of the informal description given in the first step. [ABSTRACT FROM AUTHOR]

A television-like scanned-display system has been successfully Implemented on a Honeywell DDP424 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. [ABSTRACT FROM AUTHOR]

A parsing algorithm which seems to be the most efficient general context-free algorithm known is described. It is similar to both Knuth's LR(k) algorithm and the familiar top-down algorithm. It has a time bound proportional to n3 (where n is the length of the string being parsed) in general; it has an n2 bound for unambiguous grammars; and it runs in linear time on a large class of grammars, which seems to include most practical context-free programming language grammars. In an empirical comparison it appears to be superior to the top-down and bottom-up algorithms studied by Griffiths and Petrick. [ABSTRACT FROM AUTHOR]

The article presents a partial dossier on distinguishing between handwritten zero and the letter "oh." Most standard typewriters make no distinction between the "oh" and the zero. In fact, some do not have a key for the zero, relying upon the capital "oh" instead. This is a convention rooted in time. A great deal of handset type and some typewriters differentiate by making the "oh" fatter and rounder while the zero remains a narrow oval. Some fonts have distinguished even more by making the "oh" squarish. Such a difference in character width affords partial distinction; it requires a size discrimination from the reader which requires more concentration than graphic discrimination. The slash has been used to distinguish between the "oh" and the zero. The only problem is that users have been inconsistent in deciding which of the two should be slashed. It is the existing and preferred practice that, on devices such as printers and typewriters, the character shapes for zero and oh be sufficiently different and distinguishable.

The article reports on several algorithms with their specific computational dynamics. A specific algorithm with its corresponding formula which provides for the procedure for deriving a certain value is provided. The algorithms include, among others, algorithm 290 for linear equations, algorithm 291 for logarithm of gamma functions, and algorithm 178 for direct search. Moreover, the algorithms are written in the ALGOL 60 Reference Language, Standard FORTRAN, and Basic FORTRAN. Specific instructions on how to submit algorithms are also included.

A large number of calculations in high-energy elementary particle physics involve the manipulation of complicated algebraic expressions containing both tensor and noncommutative matrix quantities. Many of these calculations take several months to complete, although the operations involved follow straightforward rules. In this paper program is described, which has been developed in LISP far solving such problems. The manner in which these problems are encountered is outlined, and their representation in the computer discussed. At present, about six months of human work takes less than Fifteen minutes on an IBM 7090. Limitations of the present system and future plans are also outlined. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented discussing the subroutines in Fortran programs.

A letter to the editor is presented in response to the article "Levels of Computer Systems," by Peter Bryant in the December 1996 issue.