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- Comments: Gated by NETNEWS@AUVM.AMERICAN.EDU
- Path: sparky!uunet!gatech!paladin.american.edu!auvm!AUVM.BITNET!HARNDEN
- Message-ID: <CSG-L%92090810375266@VMD.CSO.UIUC.EDU>
- Newsgroups: bit.listserv.csg-l
- Date: Tue, 8 Sep 1992 10:31:10 EDT
- Sender: "Control Systems Group Network (CSGnet)" <CSG-L@UIUCVMD.BITNET>
- From: eric harnden <HARNDEN@AUVM.BITNET>
- Subject: stella; the first naive question
- Lines: 52
-
- i've been working with stella on the mac for a while now, and the
- recent set of inquiries with regard to its utility in pct modeling
- motivated me to play with it. a couple of disconnected comments, and
- a question, now arise...
- 1) the last time i talked to high performance systems, they did not mention
- anything about porting stella to the pc (at least i think someone here asked
- that question). at the same time, neither is dynamo going to go to the mac.
- unfortunate, for while it is not nearly as slick, it is a lot more flexible
- in some ways.
- 2) it occurred to me that the classic systsem dynamics diagram, as developed
- by forrester, takes into account one of the central notions of pct, about which
- mr powers was trying to educate me earlier... equations which represent
- an entity's response to a change in a system level always take as input,
- not the actual state of that level, but a transformation of it, often labeled
- "perception of...".
- 3) i put the following plot into stella the other night:
-
- ║-------------------level<-------valve----------->source/sink
- ║--->perceived level /\
- ║ ║
- \/ ║
- reference----------->error--------->rate of change
- level /\
- ║
- disturbance
-
- where the only material flow is the increase/decrease of the level, and all
- other connections are information flows. the first question is: does this
- at all capture the basic pct structure (wihout the hierarchy)? it looks to
- me like the basic cybernetic structure, and follows the essentials of
- forrester's method. now, if 'the entity' is that part of the structure
- which receive the perception, contains the reference, calculates the
- error, and acts upon the rate of change, then i think i have some idea
- of the distinction between the phrases 'controlling' and 'controlling
- for'. but i might also have it all wrong. it seems to me that the entity
- is controlling the environment (acting upon the rate of change) in order
- to obtain (is controlling for) a certain perception. yes? no?
- next question: is the disturbance a disturbance of the environment, as i
- have shown it, or a disturbance of the perceptual transformation? or
- both?
- hmmm... i have also just thought of some other fundamental confusions on
- my part, not the least of which is the unclear distinction between entity
- and environment implied by the dependence of rate of change on error.
- but let's start simple, shall we?
-
- -----------< Cognitive Dissonance is a 20th Century Art Form >-----------
- Eric Harnden (Ronin)
- <HARNDEN@AUVM.BITNET> or <HARNDEN@AMERICAN.EDU>
- The American University Physics Dept.
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