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An Overview of the Computer Aided Design of Control Systems
Copyright © IFAC Software for Computer Control Madrid, Spain 1982
AN OVERVIEW OF THE COMPUTER AIDED DESIGN OF CONTROL SYSTEMS T. P. Wang Beijing Institute oJ Technology, Beijing, China
Abstract. In this paper an operview is given of the development, use and trend of the computer aided design of control systems (CADGS;. Related aspects are as follows: I. Introduction: Something about the definition of CADCS. 11. The present state of CADCS: main achievement in these years, such as interactive programs, software reliability, extensions of the field of CADCS, re a l time application. Ill. The value and the tren4s of CADCS. IV. Conclusion • •• eywords. Computer-aided design; computer-aided system' desien; control system analySiS; control system synthesis; computer programr.ling.
INTRODUCTI ON It is extremely difficult to review comprehensively current applications and development achieved in these years in such a complex and very sophisticated techniques like computer aided deSign of control systems (CADCS). So the purpose of this paper is just to provide a very brief overview of CADeS, to endeavour to describe its present state, and then to give a very short comment on trends 0: CADGS. What is CADeS? In literatures there are several different ways to define CADCS. Here only three of them are extracted. 1) "Any use of a computer to aid in control system design"! 2) "It is a technique in which man and
machine are blended in a control system designing team, intllnately coupling the best characteristics of each so that this team works better than either alone"~ Though the second one points out clearly that it is a technique, it can I t include those CADCS that there is not interactive program (we call it here tentatively the automated CADCS) in it. Therefore the second definition is only suitable to the interactive CADCS which is, of course, a very important type CADCS. The first one is too simple to understand the integration of the CADCS, though it may include either the automated type or the interactive one. So I myself prefer the following one. 3) "CADCS is equivalent to the integration of appropriate computer hardware and software modules to
238
T. P. Wang
create systems for control systems design": The third one doesn't exclude either t ype s.
section only shortly describes some main achievements in CADCS in these years.
But now I would like to propose the following one:
Interactive
"CADCS is an advanced technique which can be used to form an integ ration of appropriate computer hardware and software modules, and even inc lud i ng the user, to create systems for control system design': This definition emphasizes simultaneously the following points: 1) CADCS is an and
ad v~ nced
3) it does not exclude either types of CADCS . What I should like to note i s that the phrase "control system design" should be understo od in a broad sense. i. e., the word "design" may be replaced by one and/o r some of the follow in g rel evant termS such as analysis , Simul a ti on, pnrameter estim8 tion, i dentificati nn, modelling, synthesis , real time control, etc . ~R.ESENT
The major change and features of CADCS in recent years are the availability of graphics terminal and the interactive with the program, they can offer a higher degree of flexibility as compared to a readyto-u se progra m. They are not only used to assist the user in the design of control systems, but also they can be a very valuable tool in education ond researc h.
technique,
2) this technique c an be used to fo r m an integration of approp ri ate computer hnrdware and software modules for control system design, and
T1lli
~rograms
STATE OF CADCS
CADCS programs current available nearly cover every aspect of control systems design, such as Simulation, analys~s, i dentificati on, modelling, synthesis and real time control. This
Generally speaking , in order to get an optimal control system design, the design process often requires an interaction between the designer and program. The computer must be able to give quikly the calcul a tion consequences of, say, a chosen controller for the system response. So , two pa rts mak e this interaction pOSSible, na mely the graphi c display and the conversational mode. By which the designer and the computer communicate with each other. The display device often used may be a teletype printer, a plotter or a screen. Each device has its specific cha r acte ristics. Gene rally, there a re two types of conversational modes to be distinguished to implement the communica tion between computer and user, namely a question-answer approach (Q/A ) or a command l anguage. The latter is more suitable for CADCS prograrr. , compared with the former. Especially when the program supplies
An Overview of Computer Aided Design
the designer with information when he so requires or when he makes an error in a command string. Software Reliability At the outset the problem of software reliability was not drawn proper attention, and the users of new software typic al ly experienced very high error r a te. In addition, the object gradually recognized by the public for producing reliable software are much the same as those fo r reducing the high cost of the software. In recent years, great advances have been made in this respect~,5 One of the main measures is to make the software modu18rized. Nodularization can provide many important beni fits , some of them are: 1) easier to debug and to maintain, 2) easier to modify and to extend, 3) easier to reuse and 4) easier to be feasible. j',10d ul a rizati on also has benifits in terms of understanding, portability, robustness and testability. All of these benifits will certainly increase the software reliability. There are still some other measures to improve reliability like the structure programming, top-down with some bottom-up programmin g approach and some rules that the progr3mmer can follow to improve the programming style, etc.
239
f.lODELLING AND CONTROL OF NONTECHNICAL SYSTEMS"~ is written by J.E. Balchen (Norway). This pa per , describes an important application of CADCS technique to the modelling and estimation of the total ecological system of the Barents Sea, which is one of the most productive ocean in the world. The total model consists of a number of submodeles describing the physical oceanography (including phytoplankton), the phySiology, behav ior and population of zoo-plankt on and finally the physiology, beha viour and population of the most import ant species of fish. The purpo s e of the computer program is to arrive at an operational system which provides optimal estimates of past, present and future states of the ocean with particular to the resources of fish. The program started in 1975 and the first version of an operational system is planned to be ready by 198 5 . The physical and biologic a l processes encountered in this system are highly dynamic and the number of state variables in the different sybsystems are strongly intera cting. Some typical outputs of this CADCS facility ha ve been developed for the above purpose.
In that paper, it also describes something about modelling and control of the large scale nat ional economics. Obviously, the success of these researches and development are closely The Further Extensions of the Field dependent upon the efficiency of the of CADCS CADCS technique. So we can see that these extensions of CADCS techniques Now the field of CADCS has already are quite Significant. In addition, it extended to computer aided identificahas been recognized for many years that tion, computer-aided modelling, comthe artificial intelligence is closely puter aided estimation and so on. In related to the CADCS technique; All of recent years a number of paper related to these extensions have been published. these make CADCS technique not to be limited in a narrow sense of "control For example, the paper entitled "THE NEED FUR COMr'UTER AIDED DESIGN IN system design".
240
T. P. Wang
Controller Design in a Real Time EnvironmentS Computer-aided s ystem controller de s i gn app r oac he s can be divided into 3 different catego ri e s now? They a re 1 ) design i ng wit h th e a i d of ana lyti cal method f or s ystems with welldefin ed stru ct ure, 2j designin g by means of s i mulatio n and 3 ) design i ng i n a real -time env ironmen t. The f irs t t wo categori es a r e th e us ua l ways . The thi rd one i s ve r y usefu ll whil e a pr ocess r uns in real ti me , th e cont r olle r can be fo r c ed to do t hi s so . The ope r a tin g syst em has to s a mpl e the proce~s stotes at a gi ven i nsta n ts und Renernte an 2p~rnp r iate contro l signnl . Those two a ctions should h8:Jpen ut the s ame t i me . The ou tp ut will be delayed by a time T beca use it takes tne cor;t r olle r t he s a me time to comp ut e. As t he proce s s is fast , R large time delay wilJ can 't be accepted . So the co ntr oll er de Sign i n such ~n envi r cnment must take it into ~ ccount . Therefo r thi s category of controller desiRD i s qu i te mea llin{,;ful , too . Besiues all of the 8bo v e cited , I thin~ the r e a r e cer ta i nly mHny othe r Dchievements in the l a t est de c ades l i ke the U~ contrih utio ns on the CADC S of mult i vori able systems ( U~• '1ST) 1 0 -13 and the ava i labi l i ty of Some of t he ge ne r a l purpose s i mula t ion l Angu ages, C A ~CS on s mall er compute rs, e tc. I c an ' t li s t them one by one . 'fHE VALUE AND Tllli 'l'llliNDS OF CADCS
A lot of work have be en don e on the subj e ct--benifits CADCS c an provide for th e thr ee ma jor a rea s of education (c omp uter a i ded learnin g , co mputer
aided instructions, etc), industry and research. Excellent pa pers on these relevant topi cs can be found in the literatures. 14 - 20 For this reaso n I don't like to repeat this published ma t e ri a l s here. Instead I try to s t ate one of my own viewpoints on the benifits it can provide for research only. N.Wiener said in his "CYBERNET I CS" in 1947" ... I f I s a y tha t the first ind ustrial revolu t i on, th e r evolu ti on of t he 'dark sat anic mill s ', wa s th e devalu a tion of t he human a rm by the compe ti t i on of machin ery • ••• The modern ind us tri a l r evol uti on i s simila rly boun d t o devalu e t he human bra in Ht l eas t in i t s s imple r a nd more routin e decisi on s ". Anal or!;ou s ly s pe ak in ~ , could I SHy that today ' s technical r evo lution (th e CADCS t e chn iq ue s r ega rded a s one of its ma jor con t ents ) is si mi1 8rl y bound to devalue both the huma n bra in an d hum an a rm simult a ne ously And a step fur t her ';> Tha t meanS the CADCS t e chn i ques pl a y a very i mrort an t rol e i n developin g the r e sea r ch a nd e ven i n ca rrying forward t oda y' s techn ic a l revolution. Th e e xt en s i ons of t he fi e ld of CADCS to co mputer-aid ed ide nti f ic a ti on and c ompu t er-a i ded mo delling a r e still the constant trends in t he f uture. These will lea d to the a utomatic genera tion of mo del s . In the c om i~ g ye a rs, I do believe that CA DCS techniques will be combined with the a rti f i t i a l intelligence in an ever closer rel a tion. The applications of CADCS techniques to nontechnical large-social systems are certainly another important trend. The optimal co ntrol of such l a rge-
An Overvie w of Comput er Aided Design
scale system s is onp. of the most urgen t proble m of today. The trend for very cheap system on pocke t calcu lator is still quite new~2 It i s alread y gOing on. It is hopef ul that very soon user will ha ve a home-made CADCS packag e to deal with the contro l syst em design . ~erhaps
there are many other trends and pro bl ems in CADCS, such as the nu~ e ric 8l accura cy of progra ms, porgra ms portab ilit y and stand ardization of softwa r es , the langua ge for r eal tim e intera ction , how to get the best blend ing quali ties of the compu ter and the design er during the man -mac hine intera cti on, data base manag ement and s o on and so forth. For the space is limi too, so I can't cite them in detai l.
In the above secti ons a very short descr i ption about the curren t state of CADCS, its value and its trends a re given , becau se to review the whole f ield in detai l of CA~CS is quite diffic ult and even imposs ible. In additi on I avail mysel f of this o pportu nity to propo se some viewpo ints of mysel f. REFBRENCES 1)D.E .Ather ton. The Value of Compu ter Aided Desig n. ?roc. of the IFAC Sympo sium, ZUric h, SWitz erland , 29-31 Augus t 1919. 2)J.J. Allan 111, E .E. Found ations of The Many Manif estati ons of Compu ter Augme nted Desig n. Eroc. of the IFIP Worki ng Conf. on Princ iple of CAD. 1913. 3)J.H atvany , W.M.Newman and M.A.S abin.
241
World Survey of Compu ter Aided Desig n. Comp uter-a ided design . Volume 9 numbe r 2 April 1911. 4)D.N .Farna n. Relia ble Compu ter Software: What It Is and How To Get It. uefen se System s Manag ement Schoo l. Fort Belvo ir Virgi nia. 1915. 5)F.L .Baue r. Sof tware Enpine ering . Spring -Verla g Berlin . Heide lbe rg. 1911. 6)J.G .Balch en. The Ne ed fOr Compu te rAided DeS i gn in Model ling and Contr ol of Nonte chnica l Systern~. IFACSy r1P . 23-31 Au g . 1919 . 1 ) Jean-C laude Latom be. Arti fic ial Intel ligenc e in Compu ter-ai ded Desig n. CAD System s 1911. 8)I.Ha ntuch . Autom atic Synth esis of a Packag ed Progra m For Real Time Techn ologic al Proc eAs Contro l. Proc. of the IFAC Sympo sium. ZUrich , Switz erland , 29- 31 Augus t 1919. 9)P . E .J.Van den Bosch and ~ . M .Brui jn . Reqpir em ents and Use of CAD Programs for Cont rol System Desig n. ibid. 10)N . Munro. The U ~ IST Contr ol System DeSign and Synth esis Suite s. ibid. 11 )A.G.J .MacF arlan e . Frequ ency f·1ethod s In Mul tivari able Feedb ack System Design . lEE Conf. on CACSP . 1913 12)J. J.Bel letrut ti. Compu ter-aid ed DeSign and the Cha r acter ist ic Locus Me thod. ibid. 13)D.Q .I'layn e and S . C. Chuan g. The Seque ntial Heturn Diffe rence Method for DeSig ning Linea r Multi variab le System s. ibid. 14 )D . P .Ather ton and Celli er. Round Table Discu ssion on the Value of Compu ter Aided Desig n. Froc. of the IFAC Sympo sium. ZUric h, SWitz erland , 1919. 1S)D. P.Ath erton. The Role of CAD in
242
T. P. Wang
Education and Research, IFAC 8th Triennial World Congress Vol.XIII. 1981. Japan. 16)W.J.H.Lemmen and A.J.W.Van Den Boom. Interactive Computer Programs for Education and Research: A Survey. Automatica, Vol.1~, 1979. 17)P.AgathokliS, et al. Educational Aspects of Using Computer Aided Design in Automatic Control. ~ roc. of the IFAC Symposium, ZUrich, Switzerl~nd, 23-31 August 1979. 18 )2 .Martin Larsen. Trneds in Automatic Control Education. Automati ca , Vol.1~ 1979. 19)K .Jamsh idi, et al. ~ roblems of Automatic Control Education in Developin g Countries, ibid. 20)H .H.RosenbrocK . The Future of Control. Automatica, Vol.13 1977 • 21 )N .Wiener . Cybernet ics. John Wiley and Sons. Inc. 1948. 22)S .W.Wang ,T. p .Wang. A CAD Program Adapted to a Calculater for Digital Opt imal Control Systems. (To be 2ubl i shed) .
AN OVERVIEW OF THE COMPUTER AIDED DESIGN OF CONTROL SYSTEMS T. P. Wang Beijing Institute oJ Technology, Beijing, China
Abstract. In this paper an operview is given of the development, use and trend of the computer aided design of control systems (CADGS;. Related aspects are as follows: I. Introduction: Something about the definition of CADCS. 11. The present state of CADCS: main achievement in these years, such as interactive programs, software reliability, extensions of the field of CADCS, re a l time application. Ill. The value and the tren4s of CADCS. IV. Conclusion • •• eywords. Computer-aided design; computer-aided system' desien; control system analySiS; control system synthesis; computer programr.ling.
INTRODUCTI ON It is extremely difficult to review comprehensively current applications and development achieved in these years in such a complex and very sophisticated techniques like computer aided deSign of control systems (CADCS). So the purpose of this paper is just to provide a very brief overview of CADeS, to endeavour to describe its present state, and then to give a very short comment on trends 0: CADGS. What is CADeS? In literatures there are several different ways to define CADCS. Here only three of them are extracted. 1) "Any use of a computer to aid in control system design"! 2) "It is a technique in which man and
machine are blended in a control system designing team, intllnately coupling the best characteristics of each so that this team works better than either alone"~ Though the second one points out clearly that it is a technique, it can I t include those CADCS that there is not interactive program (we call it here tentatively the automated CADCS) in it. Therefore the second definition is only suitable to the interactive CADCS which is, of course, a very important type CADCS. The first one is too simple to understand the integration of the CADCS, though it may include either the automated type or the interactive one. So I myself prefer the following one. 3) "CADCS is equivalent to the integration of appropriate computer hardware and software modules to
238
T. P. Wang
create systems for control systems design": The third one doesn't exclude either t ype s.
section only shortly describes some main achievements in CADCS in these years.
But now I would like to propose the following one:
Interactive
"CADCS is an advanced technique which can be used to form an integ ration of appropriate computer hardware and software modules, and even inc lud i ng the user, to create systems for control system design': This definition emphasizes simultaneously the following points: 1) CADCS is an and
ad v~ nced
3) it does not exclude either types of CADCS . What I should like to note i s that the phrase "control system design" should be understo od in a broad sense. i. e., the word "design" may be replaced by one and/o r some of the follow in g rel evant termS such as analysis , Simul a ti on, pnrameter estim8 tion, i dentificati nn, modelling, synthesis , real time control, etc . ~R.ESENT
The major change and features of CADCS in recent years are the availability of graphics terminal and the interactive with the program, they can offer a higher degree of flexibility as compared to a readyto-u se progra m. They are not only used to assist the user in the design of control systems, but also they can be a very valuable tool in education ond researc h.
technique,
2) this technique c an be used to fo r m an integration of approp ri ate computer hnrdware and software modules for control system design, and
T1lli
~rograms
STATE OF CADCS
CADCS programs current available nearly cover every aspect of control systems design, such as Simulation, analys~s, i dentificati on, modelling, synthesis and real time control. This
Generally speaking , in order to get an optimal control system design, the design process often requires an interaction between the designer and program. The computer must be able to give quikly the calcul a tion consequences of, say, a chosen controller for the system response. So , two pa rts mak e this interaction pOSSible, na mely the graphi c display and the conversational mode. By which the designer and the computer communicate with each other. The display device often used may be a teletype printer, a plotter or a screen. Each device has its specific cha r acte ristics. Gene rally, there a re two types of conversational modes to be distinguished to implement the communica tion between computer and user, namely a question-answer approach (Q/A ) or a command l anguage. The latter is more suitable for CADCS prograrr. , compared with the former. Especially when the program supplies
An Overview of Computer Aided Design
the designer with information when he so requires or when he makes an error in a command string. Software Reliability At the outset the problem of software reliability was not drawn proper attention, and the users of new software typic al ly experienced very high error r a te. In addition, the object gradually recognized by the public for producing reliable software are much the same as those fo r reducing the high cost of the software. In recent years, great advances have been made in this respect~,5 One of the main measures is to make the software modu18rized. Nodularization can provide many important beni fits , some of them are: 1) easier to debug and to maintain, 2) easier to modify and to extend, 3) easier to reuse and 4) easier to be feasible. j',10d ul a rizati on also has benifits in terms of understanding, portability, robustness and testability. All of these benifits will certainly increase the software reliability. There are still some other measures to improve reliability like the structure programming, top-down with some bottom-up programmin g approach and some rules that the progr3mmer can follow to improve the programming style, etc.
239
f.lODELLING AND CONTROL OF NONTECHNICAL SYSTEMS"~ is written by J.E. Balchen (Norway). This pa per , describes an important application of CADCS technique to the modelling and estimation of the total ecological system of the Barents Sea, which is one of the most productive ocean in the world. The total model consists of a number of submodeles describing the physical oceanography (including phytoplankton), the phySiology, behav ior and population of zoo-plankt on and finally the physiology, beha viour and population of the most import ant species of fish. The purpo s e of the computer program is to arrive at an operational system which provides optimal estimates of past, present and future states of the ocean with particular to the resources of fish. The program started in 1975 and the first version of an operational system is planned to be ready by 198 5 . The physical and biologic a l processes encountered in this system are highly dynamic and the number of state variables in the different sybsystems are strongly intera cting. Some typical outputs of this CADCS facility ha ve been developed for the above purpose.
In that paper, it also describes something about modelling and control of the large scale nat ional economics. Obviously, the success of these researches and development are closely The Further Extensions of the Field dependent upon the efficiency of the of CADCS CADCS technique. So we can see that these extensions of CADCS techniques Now the field of CADCS has already are quite Significant. In addition, it extended to computer aided identificahas been recognized for many years that tion, computer-aided modelling, comthe artificial intelligence is closely puter aided estimation and so on. In related to the CADCS technique; All of recent years a number of paper related to these extensions have been published. these make CADCS technique not to be limited in a narrow sense of "control For example, the paper entitled "THE NEED FUR COMr'UTER AIDED DESIGN IN system design".
240
T. P. Wang
Controller Design in a Real Time EnvironmentS Computer-aided s ystem controller de s i gn app r oac he s can be divided into 3 different catego ri e s now? They a re 1 ) design i ng wit h th e a i d of ana lyti cal method f or s ystems with welldefin ed stru ct ure, 2j designin g by means of s i mulatio n and 3 ) design i ng i n a real -time env ironmen t. The f irs t t wo categori es a r e th e us ua l ways . The thi rd one i s ve r y usefu ll whil e a pr ocess r uns in real ti me , th e cont r olle r can be fo r c ed to do t hi s so . The ope r a tin g syst em has to s a mpl e the proce~s stotes at a gi ven i nsta n ts und Renernte an 2p~rnp r iate contro l signnl . Those two a ctions should h8:Jpen ut the s ame t i me . The ou tp ut will be delayed by a time T beca use it takes tne cor;t r olle r t he s a me time to comp ut e. As t he proce s s is fast , R large time delay wilJ can 't be accepted . So the co ntr oll er de Sign i n such ~n envi r cnment must take it into ~ ccount . Therefo r thi s category of controller desiRD i s qu i te mea llin{,;ful , too . Besiues all of the 8bo v e cited , I thin~ the r e a r e cer ta i nly mHny othe r Dchievements in the l a t est de c ades l i ke the U~ contrih utio ns on the CADC S of mult i vori able systems ( U~• '1ST) 1 0 -13 and the ava i labi l i ty of Some of t he ge ne r a l purpose s i mula t ion l Angu ages, C A ~CS on s mall er compute rs, e tc. I c an ' t li s t them one by one . 'fHE VALUE AND Tllli 'l'llliNDS OF CADCS
A lot of work have be en don e on the subj e ct--benifits CADCS c an provide for th e thr ee ma jor a rea s of education (c omp uter a i ded learnin g , co mputer
aided instructions, etc), industry and research. Excellent pa pers on these relevant topi cs can be found in the literatures. 14 - 20 For this reaso n I don't like to repeat this published ma t e ri a l s here. Instead I try to s t ate one of my own viewpoints on the benifits it can provide for research only. N.Wiener said in his "CYBERNET I CS" in 1947" ... I f I s a y tha t the first ind ustrial revolu t i on, th e r evolu ti on of t he 'dark sat anic mill s ', wa s th e devalu a tion of t he human a rm by the compe ti t i on of machin ery • ••• The modern ind us tri a l r evol uti on i s simila rly boun d t o devalu e t he human bra in Ht l eas t in i t s s imple r a nd more routin e decisi on s ". Anal or!;ou s ly s pe ak in ~ , could I SHy that today ' s technical r evo lution (th e CADCS t e chn iq ue s r ega rded a s one of its ma jor con t ents ) is si mi1 8rl y bound to devalue both the huma n bra in an d hum an a rm simult a ne ously And a step fur t her ';> Tha t meanS the CADCS t e chn i ques pl a y a very i mrort an t rol e i n developin g the r e sea r ch a nd e ven i n ca rrying forward t oda y' s techn ic a l revolution. Th e e xt en s i ons of t he fi e ld of CADCS to co mputer-aid ed ide nti f ic a ti on and c ompu t er-a i ded mo delling a r e still the constant trends in t he f uture. These will lea d to the a utomatic genera tion of mo del s . In the c om i~ g ye a rs, I do believe that CA DCS techniques will be combined with the a rti f i t i a l intelligence in an ever closer rel a tion. The applications of CADCS techniques to nontechnical large-social systems are certainly another important trend. The optimal co ntrol of such l a rge-
An Overvie w of Comput er Aided Design
scale system s is onp. of the most urgen t proble m of today. The trend for very cheap system on pocke t calcu lator is still quite new~2 It i s alread y gOing on. It is hopef ul that very soon user will ha ve a home-made CADCS packag e to deal with the contro l syst em design . ~erhaps
there are many other trends and pro bl ems in CADCS, such as the nu~ e ric 8l accura cy of progra ms, porgra ms portab ilit y and stand ardization of softwa r es , the langua ge for r eal tim e intera ction , how to get the best blend ing quali ties of the compu ter and the design er during the man -mac hine intera cti on, data base manag ement and s o on and so forth. For the space is limi too, so I can't cite them in detai l.
In the above secti ons a very short descr i ption about the curren t state of CADCS, its value and its trends a re given , becau se to review the whole f ield in detai l of CA~CS is quite diffic ult and even imposs ible. In additi on I avail mysel f of this o pportu nity to propo se some viewpo ints of mysel f. REFBRENCES 1)D.E .Ather ton. The Value of Compu ter Aided Desig n. ?roc. of the IFAC Sympo sium, ZUric h, SWitz erland , 29-31 Augus t 1919. 2)J.J. Allan 111, E .E. Found ations of The Many Manif estati ons of Compu ter Augme nted Desig n. Eroc. of the IFIP Worki ng Conf. on Princ iple of CAD. 1913. 3)J.H atvany , W.M.Newman and M.A.S abin.
241
World Survey of Compu ter Aided Desig n. Comp uter-a ided design . Volume 9 numbe r 2 April 1911. 4)D.N .Farna n. Relia ble Compu ter Software: What It Is and How To Get It. uefen se System s Manag ement Schoo l. Fort Belvo ir Virgi nia. 1915. 5)F.L .Baue r. Sof tware Enpine ering . Spring -Verla g Berlin . Heide lbe rg. 1911. 6)J.G .Balch en. The Ne ed fOr Compu te rAided DeS i gn in Model ling and Contr ol of Nonte chnica l Systern~. IFACSy r1P . 23-31 Au g . 1919 . 1 ) Jean-C laude Latom be. Arti fic ial Intel ligenc e in Compu ter-ai ded Desig n. CAD System s 1911. 8)I.Ha ntuch . Autom atic Synth esis of a Packag ed Progra m For Real Time Techn ologic al Proc eAs Contro l. Proc. of the IFAC Sympo sium. ZUrich , Switz erland , 29- 31 Augus t 1919. 9)P . E .J.Van den Bosch and ~ . M .Brui jn . Reqpir em ents and Use of CAD Programs for Cont rol System Desig n. ibid. 10)N . Munro. The U ~ IST Contr ol System DeSign and Synth esis Suite s. ibid. 11 )A.G.J .MacF arlan e . Frequ ency f·1ethod s In Mul tivari able Feedb ack System Design . lEE Conf. on CACSP . 1913 12)J. J.Bel letrut ti. Compu ter-aid ed DeSign and the Cha r acter ist ic Locus Me thod. ibid. 13)D.Q .I'layn e and S . C. Chuan g. The Seque ntial Heturn Diffe rence Method for DeSig ning Linea r Multi variab le System s. ibid. 14 )D . P .Ather ton and Celli er. Round Table Discu ssion on the Value of Compu ter Aided Desig n. Froc. of the IFAC Sympo sium. ZUric h, SWitz erland , 1919. 1S)D. P.Ath erton. The Role of CAD in
242
T. P. Wang
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