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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