RE: Friam Digest, Vol 21, Issue 14

[Nick Thompson]

Robert,

I realize I may be climbing on this subthread a little late, but isnt that
just eliminating agent based modeling on idealogical grounds..... If I cant
differentiate it I aint interested in it.   this would be different than my
Clark colleague's claim that ABM's are just not.....mathematical.

NIck

Nicholas S. Thompson
Professor of Psychology and Ethology
Clark University
[hidden email]
http://home.earthlink.net/~nickthompson/
 [hidden email]

> [Original Message]
> From: <[hidden email]>
> To: <[hidden email]>
> Date: 3/13/2005 9:00:27 AM
> Subject: Friam Digest, Vol 21, Issue 14
>
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> Today's Topics:
>
>    1. self organizing language (Roger Critchlow)
>    2. St. Johns (Nicholas Thompson)
>    3. RE: Mathematics VS? Agent Based Modeling (Robert Holmes)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Sat, 12 Mar 2005 14:15:26 -0700
> From: Roger Critchlow <[hidden email]>
> Subject: [FRIAM] self organizing language
> To: [hidden email]
> Message-ID: <[hidden email]>
> Content-Type: text/plain; charset=US-ASCII
>
> A friend sent me this link:
>
> http://www.sciencedaily.com/releases/2005/02/050223150852.htm
>
> The proposal is that the grammatical forms of languages are emergent
> from simpler rules.
>
> -- rec --
>
>
>
> ------------------------------
>
> Message: 2
> Date: Sat, 12 Mar 2005 14:16:23 -0700
> From: "Nicholas Thompson" <[hidden email]>
> Subject: [FRIAM] St. Johns
> To: "Friam" <[hidden email]>
> Message-ID: <[hidden email]>
> Content-Type: text/plain; charset="us-ascii"
>
> So, who is going to bell the cat.  St. Johns can be ferocious in its own

way .... so we need somebody with extraordinarily good manners, a light
touch, great leadership skills, and a name like Guerin.  Hmmmm.  Who could
we think of that would fit that bill.    I would be happy to contribute to
a St. Johns WIFI point, but I can imagine it might take a little time.  I
can imagine the Dean wondering if we really WANT web access  on all over
campus.  

>
> Has nobody invented a portable WIFI point yet?  
>
> Nick
>
>
>
>
> Nicholas S. Thompson
> Professor of Psychology and Ethology
> Clark University
> [hidden email]
> http://home.earthlink.net/~nickthompson/
> [hidden email]
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> ------------------------------
>
> Message: 3
> Date: Sun, 13 Mar 2005 07:14:58 -0700
> From: "Robert Holmes" <[hidden email]>
> Subject: RE: [FRIAM] Mathematics VS? Agent Based Modeling
> To: "'The Friday Morning Applied Complexity Coffee Group'"
> <[hidden email]>
> Message-ID: <[hidden email]>
> Content-Type: text/plain; charset="US-ASCII"
>
> My loose use of terminology (OK, wrong) didn't help there - yes, all the
> examples quoted so far have been closed-loop systems because yes, the
> outputs all effect subsequent inputs to the system (assuming those
> supply-chain clients actually pay attention to my advice).
>
> However Parunak makes a stronger claim: that ABMs can be used for
> *automatic* closed-loop control: "...a control scheme that more or less
> automatically regulates the behavior of the entire system." In other

words,
> we can use ABMs where the feedback loop is not mediated by a human. And
> (IMHO) this is a big and unsupported claim. So to rephrase my question,
are
> there any real-world examples of using an ABM in a *automatic* closed-loop
> control system?
>
> My facetious comments about using NetLogo to run my car's control systems
> got in the way of a real question. In automatic closed-loop control, I
want
> to be able to write a differential equation that describes the system
> (feedback loop included) and then solve it. I want to determine whether
the
> controller diverges or convereges, whether solutions exist, whether they
are
> oscillatory, what the controller's safe (non-divergent) range of operation
> is and so on. Now if I'm using equation-based models, I've a fair chance
of
> doing that. But if I'm using agent-based models which might (or might not)
> show sensitivity to intial conditions, which might (or might not) be
> stochastic and give multi-valued solutions, what do I do? As Owen once
> succinctly put it, how do I differentiate an ABM?
>
> And this is the reason I think Parunak's claim is too strong: if you try
to
> design an automatic closed-loop control system with an ABM at its heart,
you
> don't have access to all the tools and methodologies that enable you to
> assess the controller's stability and robustness. And if the designer
can't
> assess a controller's stability and robustness s/he is unlikely to
implement

> it in a real-world application.
>
> Robert
>
>  
>
> > -----Original Message-----
> > From: Raymond Parks [mailto:[hidden email]]
> > Sent: Friday, March 11, 2005 3:22 PM
> > To: The Friday Morning Applied Complexity Coffee Group
> > Subject: Re: [FRIAM] Mathematics VS? Agent Based Modeling
> >
> > Robert Holmes wrote:
> >
> > > The distinction between open and close loop systems reminds
> > me of the
> > > distinction between asking forgiveness and asking permission. An
> > > open-loop system produces some recommended set of parameter
> > settings
> > > that a third party (usually human) can choose to implement
> > or not. A
> > > closed-loop system calculates the parameter settings then
> > goes ahead and applies them anyway.
> > > When I use an ABM to predict the bottlenecks in a supply
> > chain and I
> > > then present the results to the client, that's an open-loop system.
> > > When the EBM in my car's engine management system detects that I've
> > > done something dumb and turns on the ABS, that's a
> > closed-loop system.
> >
> >    I don't know enough about the example I gave (having only
> > read the sales literature) to say whether it is open or
> > closed loop.  Formally, of course, open-loop means that the
> > output of the controller does not affect the input while
> > closed-loop means that the output of the controller affects
> > the input.  Whether a human acts as the controller is not a
> > way to distinguish between open and closed loop control.
> >
> >    When the burger-flipper behind the counter of a fast-food
> > joint fills your drink, putting a cup under the automatic
> > faucet and pressing the button for the right size - that is
> > open loop control.  The output (soda into the drink) does not
> > affect the input (button pressed).  Conversely, when you walk
> > up to the drink fountain and refill your drink, that is
> > closed loop control with a human controller.  The output (how
> > much soda is in the glass) affects the input (whether you
> > hold the valve open).
> >
> >    Both of your examples above are closed-loop control
> > systems, whether or not your client changes their supply chain.
> >
> > > (Simulators fall in an interesting grey area: is a simulator an
> > > example of control system or an example of a simulation of
> > a control
> > > system? These are different, especially when things go pear-shaped.)
> >
> >    If one takes the long view, simulators that are used in
> > support of decision-making are closed-loop control systems.  
> > The closure is not hard-wired, but it exists.
> >
> > > So my contention is that while ABMs may be great for advisory,
> > > open-loop systems they just aren't robust enough to form
> > the core of a
> > > closed-loop system. How would you feel if the automatic control
> > > systems in your car (plane, nuclear reactor etc.) where all
> > written in
> > > NetLogo? ;)
> >
> >    Irrelevant.  How would you feel if your car/plane/nuclear
> > reactor control system was written in Visual Basic?  Both VB
> > and NetLogo are not intended for real-time systems.  For a
> > control system, one would use ABM written to satisfy the
> > timing requirements of the system.  An ABM can be written in
> > C or assembly language, if necessary to satisfy the requirements.
> >
> >    Many years ago and several previous lives, I worked on a
> > satellite control system.  The subsystem that controlled the
> > ground antenna tracking the satellite had three modes of
> > operation - signal maximizing, predicted track, and joystick.
> >  Of these, the first and last were closed loop control, while
> > the predicted track could be considered an open loop ABM (if
> > you tilt your head and squint your eyes just right) control
> > system.  All of these were written in assembly language.
> >
> >    Back in the early 90s, I used an expert system to track
> > vehicles from dumb sensor data.  The prototype expert system
> > was written in Lisp (or maybe Prolog, I can't remember for
> > sure).  The operational system used and expert system written
> > in C (right here in ABQ).  The reason for the latter was
> > simple - real-time performance.
> >
> > --
> > Ray Parks                   [hidden email]
> > IDART Project Lead          Voice:505-844-4024
> > IORTA Department            Fax:[phone]
> > http://www.sandia.gov/idart Pager:800-690-5288
> >
> >
> > ============================================================
> > FRIAM Applied Complexity Group listserv
> > Meets Fridays 9AM @ Jane's Cafe
> > Lecture schedule, archives, unsubscribe, etc.:
> > http://www.friam.org
> >
> >
> >
>
>
>
>
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> End of Friam Digest, Vol 21, Issue 14
> *************************************

[Roger Critchlow]

Actually, I think Robert's gone overboard.  We have examples of
chaotic systems which are amenable to closed loop control.  That is,
these are systems which have perfectly differentiable dynamics, but we
can't measure the state of the system with sufficient accuracy to
predict their futures to save our lives, but we can still whack the
systems hard enough and in the right direction often enough to keep
them working.

It doesn't matter where I picked this up, google returns about 728,000
results for "chaotic system control", so there are certainly more than
a few examples of chaotic systems engineering to refute that part of
Robert's claim.

So what else about ABM's disqualifies them for use in closed loop real
time control systems?

-- rec --

On Mon, 14 Mar 2005 12:24:40 -0700, Nicholas Thompson
<[hidden email]> wrote:
> Robert,
>
> I realize I may be climbing on this subthread a little late, but isnt that
> just eliminating agent based modeling on idealogical grounds..... If I cant
> differentiate it I aint interested in it.   this would be different than my
> Clark colleague's claim that ABM's are just not.....mathematical.
>
> NIck

[Robert Holmes]

I'm not sure we're talking about the same thing - isn't chaotic system
control an example of equation-based modeling?

The links I've looked at seem to be of two types: (1) the authors explicitly
write down the system's equations, those equations show chaotic behaviour
and the authors describe (adaptive) controllers that can control that
chaotic behaviour by feeding back some error term; (2) similar to the above
but the authors first have to fit observed data to some assumed equation.

Either way, it's equation based. What I've not found is someone who has
successfully done the above using an ABM at its core rather than an equation
or equations.

Still looking to have my claim refuted...

Robert

> -----Original Message-----
> From: Roger Critchlow [mailto:[hidden email]]
> Sent: Monday, March 14, 2005 2:44 PM
> To: [hidden email]; The Friday Morning Applied
> Complexity Coffee Group
> Subject: Re: [FRIAM] RE: Friam Digest, Vol 21, Issue 14
>
> Actually, I think Robert's gone overboard.  We have examples
> of chaotic systems which are amenable to closed loop control.
>  That is, these are systems which have perfectly
> differentiable dynamics, but we can't measure the state of
> the system with sufficient accuracy to predict their futures
> to save our lives, but we can still whack the systems hard
> enough and in the right direction often enough to keep them working.
>
> It doesn't matter where I picked this up, google returns
> about 728,000 results for "chaotic system control", so there
> are certainly more than a few examples of chaotic systems
> engineering to refute that part of Robert's claim.
>
> So what else about ABM's disqualifies them for use in closed
> loop real time control systems?
>
> -- rec --
>
> On Mon, 14 Mar 2005 12:24:40 -0700, Nicholas Thompson
> <[hidden email]> wrote:
> > Robert,
> >
> > I realize I may be climbing on this subthread a little
> late, but isnt
> > that just eliminating agent based modeling on idealogical
> grounds..... If I cant
> > differentiate it I aint interested in it.   this would be
> different than my
> > Clark colleague's claim that ABM's are just not.....mathematical.
> >
> > NIck
>
> ============================================================
> FRIAM Applied Complexity Group listserv
> Meets Fridays 9AM @ Jane's Cafe
> Lecture schedule, archives, unsubscribe, etc.:
> http://www.friam.org
>
>