PACTOLUS(ID:449/pac007)Digital simulation languagepresumably from the Pactolus River where King Croesus (as in "rich as Croesus") washed to lose his golden touch, hence presumably in rivalry to MIDAS Digital simulation language Brennan IBM 1964 Places
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References: Introduction Perhaps the most formidable challenge in the field of digital computer applications is the development of equipment and programs which will extend the creative power of scientific users. The crux of the problem, of course, is Intimate man-machine communication - a most elusive and difficult-to-define characteristic. The engineer requires a conveniently manageable system; the scientist requires sufficient intimacy to provide real insight into the complex interplay of problem variables; the creative user requires computing power and flexibility to permit imaginative use of the computer and graphic display to permit recognition of inventive solutions. The development of computers designed specifically for such applications has been slow due to the difficulty of ascertaining the proper man-machine relationship. Simulation is perhaps unique. It does require close man-machine communication but the nature of this interplay is fairly well known. Years of experience are available in which analog computers were used for simulation in the entire spectrum of scientific disciplines. The structural organization of the analog computer - its collection of specialized computing elements which can be interconnected in almost any desired configuration - makes it a most flexible tool for the engineer, who is trained to visualize a system as a complex of subsystems. The forte of the analog computer is in the very intimacy of the man-machine communication it permits. Since the nature of the task can be so well defined for this particular application, digital simulation seems a most logical starting point in the quest for more creative use of computers. Only when we are able to perform this task well - with ease and flexibility comparable to simulation using analog computers - only then, should me proceed to those applications where the man-machine relationship is more nebulous. Digital analog simulator programs - programs which affect the elements and organization of analog computers - are no novelty. Since the first attempt by Selfridge in 1955, there have appeared a number of such programs; best known perhaps are DEPI I, ASTRAL, DEPI 4, DYSAC, PARTNER, DAS, JANIS, and MIDAS. Significant improvements have been made in both the interconnection languages and the computational aspects. The latest and most sophisticated of these programs is MIDAS; it incorporates the best features of its predecessors while presenting several important innovations. However, all these previous programs seem to share a common failing in that while they succeed to a greater or lesser extent in using block-oriented languages to express the simulation configuration, they fail to provide the on-line operational flexibility of the analog computer. PACTOLUS is an attempt to focus attention Extract: Summary Summary Our objective in developing PACTOLUS has been twofold: to make a critical evaluation of the various techniques employed in previous digital analog simulator programs and to demonstrate that a modus operandi comparable to that of analog computer users could be obtained for digital simulation. PACTOLUS embodies the conclusions of that evaluation. No attempt has been made herein to detail the reasons for accepting certain features while rejecting others. With the hope that this effort will be of value in the development of subsequent simulation programs, we merely wish to state that this is our considered. opinion after serious study. Whether PACTOLUS does indeed represent an innovation in operational flexibility will only be known after the program achieves much wider usage. It has been used for a number of small applications, but we readily admit a measure of bias. We do feel that PACTOLUS demonstrates that our objective can be obtained. To the user of the small scientific computer, the program offers a means of conveniently solving many of those problems for which an analog computer would otherwise have been required. The techniques employed in PACTOLUS are hopefully suggestive of the manner in which digital simulation might be provided at remote terminals serviced by a large digital computer. It is our thought that digital simulation is 011 the brink of significant expansion. The availability of appropriate terminals and visual display units will herald this event. in [AFIPS JCC 26] Proceedings of the 1964 Fall Joint Computer Conference FJCC 1964 view details in [AFIPS JCC 26] Proceedings of the 1964 Fall Joint Computer Conference FJCC 1964 view details in Simulation 3(2) August 1964 view details in Simulation 3(2) August 1964 view details in Simulation 3(6) December 1964 view details Introduction The possibility of using a digital computer to obtain check solutions for the analog was recognized by many people at the dawn of our 15 year old history. Unfortunately several problems existed then, mainly at the digital end, which made this impracticable. Digital computers of that day were terribly slow, of small capacity and painfully primitive in their programming methods. It was usually the case when a digital check solution was sought for an incoming analog problem, that it was several months after the problem had been solved on the analog computer and the results turned over to the customer before the digital check solution made its appearance. The fact that the two solutions hardly ever agreed was another deterrent to the employment of this system. As we all know, digital computers have made tremendous strides in speed, capacity and programmability. In the area of programming ?and throughout this pa per - we're talking of scientific problems expressible as differential equations; the main effort has been in the construction of languages such as Fortran. Algol, etc. to permit entering the problem in a quasi-mathematical form, with the machine taking over the job of converting these to the individual serial elemental steps. While the progress along this line has been truly awe-inspiring to an analog man (usually all engineer), the resulting language has become quite foreign to him so that if he wishes to avail himself of the digital computer he must normally enjoy an interpreter in the form of a digital programmer (usually a mathematician). This means that he must describe his engineering problem in the required form, detail, and with sufficient technical insight to have the digital programmer develop a workable program on the first try. This doesn't happen very often and it is the consensus of opinion among computing facility managers that a major source of the difficulty lies in the fact that the engineer does not always realize the full mathematical implications of his problem. For example, ill specifying that a displacement is limited, he might not state what happens to the velocity. This can lead to all sorts of errors as an analog programmer would know. It is, of course, possible for an analog programmer to learn to program a digital computer by studying Fortran. This has been attempted here at Wright-Patterson AF Base with little success, mainly because, unless used very often, the knowledge is lost so that each time a considerable relearning period is required. Some computing facilities have even embarked on cross-training programs so that each type of programmer knows the other's methods. While this has much to 1,ecommend it, it is often impracticable. In March of 1963, Mr. Roger Gaskill of Martin-Orlando explained to us the operation of DAS (Digital Analog Simulator), a block diagram type of digital program which he intended for use by control system engineers who did not have ready access to an analog computer. We immediately recognized in this type of program the possibility of achieving our long-sought goal of a means to obtain digital check solutions to our analog problems by having the analog programmer program the digital computer himself! We found that our analog engineers became quite proficient in the use of DAS after about one hour's training and were obtaining digital solutions that checked those of the analog. At this point several limitations of this entire method should be acknowledged. First, the idea that obtaining agreement between the digital and analog solutions is very worthwhile is based mainly on an intuitive approach. After all both solutions could be wrong since the same programming error could be made in both. Secondly, the validity of the mathematical model is not checked, merely the computed solution. Finally, it might be argued that the necessity of the analog man communicating the problem to his digital counterpart has the value of making him think clearly and organize his work well. This is lost if he programs the digital computer himself. In spite of these limitations we thought it wise to pursue this idea. Although DAS triggered our activity in the field of analog-type digital programs, several others preceded it. A partial list of these and other such programs would include: DEPI California Institute of Technology DYSAC University of Wisconsin DIDAS Lockheed-Georgia PARTNER Honeywell Aeronautical Division DYNASAR General Electric, Jet Engine Division Almost all of these - with the possible exception of PARTNER (Proof of Analog Results Through a Numerical Equivalent Routine) - had as their prime purpose the avoidance of the analog computer. They merely wished to borrow the beautifully simple programming techniques of the electronic differential analyzer and apply them to the digital computer. While DAS proved to be very useful to us, certain basic modifications were felt to be necessary to tailor it better to our needs. Principal among these modifications was a rather sophisticated integration routine to replace the simple fixed interval rectangular type of DAS. Other important changes were made but the change in the integration scheme and our wish to acknowledge our debt to DAS, led us to the choice of the name MIDAS, an acronym meaning Modified Integration Digital Analog Simulator. In this paper a brief description of the method of using MIDAS will be given, followed by a summary of our experience in using it in a large analog facility for about 18 months. in [AFIPS JCC 26] Proceedings of the 1964 Fall Joint Computer Conference FJCC 1964 view details in Simulation 5(5) May 1965 view details in Proceedings of the IBM scientific computing symposium on digital simulation of continuous systems 1965 view details in Simulation 4(6) June 1965 view details in ACM Computing Reviews 6(04) July-August 1965 view details in [ACM] CACM 9(10) October 1966 view details in Simulation 6(1) January 1966 view details in Proceedings of the IBM scientific computing symposium on digital simulation of continuous systems 1965 view details in Proceedings of the IBM scientific computing symposium on digital simulation of continuous systems 1965 view details According to the author, "APL was conceived . . . to satisfy the need for convenient data association and data handling techniques in a high-level language. Standing for Associative Programming Language, it is designed to be embedded in PL/I as an aid to the user dealing with data structures in which associations are expressed." APL introduces a data structure called an ENTITY. A SET is a set of entities linked to each other in a ring structure. Sets may belong to an ENTITY, and an entity may be a member of a number of Sets. An Entity contains pointers to the first entity in each of its Subsets, and to the "next" member of any Set to which it belongs. An Entity also contains direct attributes, i.e., attributes that pertain to that one entity, and it may contain associative attributes which express relationships between Entities, or between an Entity and a set of which it is a member. An example of an associative attribute might be the attribute "distance" which would express a relationship between two Entities point (1) and point (2). The language has a number of statement types for creating and manipulating Entities and Sets; APL language statements are intermixed with PL/I statements. The APL processor accepts this mixture and creates therefrom a program consisting of PL/I statements and subroutine calls. In some other contexts, the word "generator" has been used to describe this kind of processor. The paper is a concise, interesting presentation of a type of system that may prove to be very useful. This reviewer has one suggestion that is offered quite seriously, though some readers might consider it frivolous. There already exists at least one language that is reasonably well known by its acronym APL. I refer to the language developed by Iverson for which translators and interpreters have been written on a number of computers. It would be helpful if the authors of the present article could make some minor change in the name of their processor to remove this very global ambiguity. in ACM Computing Reviews 8(05) September-October 1967 view details in ACM Computing Reviews 8(05) September-October 1967 view details in ACM Computing Reviews 8(05) September-October 1967 view details The author makes a strong point that the use of a small, comparatively cheap digital computer for simulation leads to a great improvement in man/machine communication when compared to the use of a large digital computer. There is no discussion of the problems of numerical instability although the third example is bothered bv the effect, which this reviewer has found to be a major nuisance in the use of digital simulation. in ACM Computing Reviews 9(08) August 1968 view details in [AFIPS] Proceedings of the 1969 Fall Joint Computer Conference FJCC 35 view details PACTOLUS was introduced in 1964 by Brennan and Sano [15] of IBM San Jose as an attempt to make a small-scale general-purpose digital computer act like an analog computer. It was written in FORTRAN II-D for the IBM 1620 computer with the 1627 plotter and a card read-punch. This work was significant in two respects. It provided the 1620 computer users a possibility of using digital analog simulation. More significantly, it demonstrated the potential of on-line digital analog simulation, as remote terminals, visual displays, and multiprogramming were just over the horizon in [AFIPS] Proceedings of the 1969 Fall Joint Computer Conference FJCC 35 view details in [AFIPS] Proceedings of the 1969 Fall Joint Computer Conference FJCC 35 view details In addition to the discussion of HYPAC, several applications are described. The paper may be of considerable practical significance. Extract: HYPAC This paper describes a hybrid computer program called HYPAC for simulating circuits and systems that have a nodular structure. Basically, a subeircuit or subsystem is patched onto the analog computer and multiplexed by the digital computer to form the required number of subeireuits or subsystems. For purposes of flexibility, HYPAC makes use of PACTOLUS, a block-oriented digital program. In addition to the discussion of HYPAC, several applications are described. The paper may be of considerable practical significance. in [AFIPS] Proceedings of the 1969 Fall Joint Computer Conference FJCC 35 view details [321 programming languages with indication of the computer manufacturers, on whose machinery the appropriate languages are used to know. Register of the 74 computer companies; Sequence of the programming languages after the number of manufacturing firms, on whose plants the language is implemented; Sequence of the manufacturing firms after the number of used programming languages.] in [AFIPS] Proceedings of the 1969 Fall Joint Computer Conference FJCC 35 view details in Computers & Automation 21(6B), 30 Aug 1972 view details The exact number of all the programming languages still in use, and those which are no longer used, is unknown. Zemanek calls the abundance of programming languages and their many dialects a "language Babel". When a new programming language is developed, only its name is known at first and it takes a while before publications about it appear. For some languages, the only relevant literature stays inside the individual companies; some are reported on in papers and magazines; and only a few, such as ALGOL, BASIC, COBOL, FORTRAN, and PL/1, become known to a wider public through various text- and handbooks. The situation surrounding the application of these languages in many computer centers is a similar one. There are differing opinions on the concept "programming languages". What is called a programming language by some may be termed a program, a processor, or a generator by others. Since there are no sharp borderlines in the field of programming languages, works were considered here which deal with machine languages, assemblers, autocoders, syntax and compilers, processors and generators, as well as with general higher programming languages. The bibliography contains some 2,700 titles of books, magazines and essays for around 300 programming languages. However, as shown by the "Overview of Existing Programming Languages", there are more than 300 such languages. The "Overview" lists a total of 676 programming languages, but this is certainly incomplete. One author ' has already announced the "next 700 programming languages"; it is to be hoped the many users may be spared such a great variety for reasons of compatibility. The graphic representations (illustrations 1 & 2) show the development and proportion of the most widely-used programming languages, as measured by the number of publications listed here and by the number of computer manufacturers and software firms who have implemented the language in question. The illustrations show FORTRAN to be in the lead at the present time. PL/1 is advancing rapidly, although PL/1 compilers are not yet seen very often outside of IBM. Some experts believe PL/1 will replace even the widely-used languages such as FORTRAN, COBOL, and ALGOL.4) If this does occur, it will surely take some time - as shown by the chronological diagram (illustration 2) . It would be desirable from the user's point of view to reduce this language confusion down to the most advantageous languages. Those languages still maintained should incorporate the special facets and advantages of the otherwise superfluous languages. Obviously such demands are not in the interests of computer production firms, especially when one considers that a FORTRAN program can be executed on nearly all third-generation computers. The titles in this bibliography are organized alphabetically according to programming language, and within a language chronologically and again alphabetically within a given year. Preceding the first programming language in the alphabet, literature is listed on several languages, as are general papers on programming languages and on the theory of formal languages (AAA). As far as possible, the most of titles are based on autopsy. However, the bibliographical description of sone titles will not satisfy bibliography-documentation demands, since they are based on inaccurate information in various sources. Translation titles whose original titles could not be found through bibliographical research were not included. ' In view of the fact that nany libraries do not have the quoted papers, all magazine essays should have been listed with the volume, the year, issue number and the complete number of pages (e.g. pp. 721-783), so that interlibrary loans could take place with fast reader service. Unfortunately, these data were not always found. It is hoped that this bibliography will help the electronic data processing expert, and those who wish to select the appropriate programming language from the many available, to find a way through the language Babel. We wish to offer special thanks to Mr. Klaus G. Saur and the staff of Verlag Dokumentation for their publishing work. Graz / Austria, May, 1973 in Computers & Automation 21(6B), 30 Aug 1972 view details in Computers & Automation 21(6B), 30 Aug 1972 view details |