Re Jay Forrests posting SD0130
Jay,
I now understand what you meant by contraction. (Ed G. was faster on
the uptake than I was). I agree.
Regards,
Jim
Semantics HELP! Re: "SD is not DiffEq"
-
Jim Hines
- Senior Member
- Posts: 80
- Joined: Fri Mar 29, 2002 3:39 am
-
Bill Harris
- Member
- Posts: 31
- Joined: Fri Mar 29, 2002 3:39 am
Semantics HELP! Re: "SD is not DiffEq"
Jay wrote:
>It appears to me that the "boom" in popularity since Senges book has
>resulted in a lot of different descriptions of the field - some of which are
>somewhat in contradiction. As the field becomes "muddy" from confusion
Yes. I see an increasing number of people who claim that causal loop
diagrams are all one needs to worry with. While I accept that the
archetypes are useful, I also accept the notion that, in general, we arent
good at estimating the temporal dynamics of complex systems.
>The contraction I see happening here is that the debate is helping a lot of
>us lurkers (like me) who are relatively self-trained hone our understaning
>of the field and to move toward a "core" understanding. That contraction
To that point, thanks to whomever posted the "Desert Island Dynamics"
pointer. Im planning on catching up on some of the study I havent done
yet.
Finally, it seems that the discussion on discrete vs. continuous has
sometimes mixed that dichotomy with feedback vs. open loop. It seems that
the software Ive seen usually joins continuous and feedback OR discrete
and open loop. I conjecture that there are times when feedback would be
nice to have in the discrete case. For example, Ive done some modeling
work (discrete) to understand and improve the way we design printed circuit
boards. The quantities are small enough so that its hard to think of
"smoothing" it all into a continuous process. However, there are feedback
effects we ignored, because the software we used didnt express those
notions. I could have coded it using Fishwicks multi-modeling approach
using SimPack, but graphical tools are nice when communicating the results
with others.
(Yes, I did hear the comment from someone far more experienced than I that
the feedback/discrete case has occurred rarely in his experience; Im just
thinking out loud, as it were.)
Regards,
Bill
--
Bill Harris Hewlett-Packard Co.
R&D Productivity Department Lake Stevens Division
domain: billh@lsid.hp.com M/S 330
phone: (206) 335-2200 8600 Soper Hill Road
fax: (206) 335-2828 Everett, WA 98205-1298
>It appears to me that the "boom" in popularity since Senges book has
>resulted in a lot of different descriptions of the field - some of which are
>somewhat in contradiction. As the field becomes "muddy" from confusion
Yes. I see an increasing number of people who claim that causal loop
diagrams are all one needs to worry with. While I accept that the
archetypes are useful, I also accept the notion that, in general, we arent
good at estimating the temporal dynamics of complex systems.
>The contraction I see happening here is that the debate is helping a lot of
>us lurkers (like me) who are relatively self-trained hone our understaning
>of the field and to move toward a "core" understanding. That contraction
To that point, thanks to whomever posted the "Desert Island Dynamics"
pointer. Im planning on catching up on some of the study I havent done
yet.
Finally, it seems that the discussion on discrete vs. continuous has
sometimes mixed that dichotomy with feedback vs. open loop. It seems that
the software Ive seen usually joins continuous and feedback OR discrete
and open loop. I conjecture that there are times when feedback would be
nice to have in the discrete case. For example, Ive done some modeling
work (discrete) to understand and improve the way we design printed circuit
boards. The quantities are small enough so that its hard to think of
"smoothing" it all into a continuous process. However, there are feedback
effects we ignored, because the software we used didnt express those
notions. I could have coded it using Fishwicks multi-modeling approach
using SimPack, but graphical tools are nice when communicating the results
with others.
(Yes, I did hear the comment from someone far more experienced than I that
the feedback/discrete case has occurred rarely in his experience; Im just
thinking out loud, as it were.)
Regards,
Bill
--
Bill Harris Hewlett-Packard Co.
R&D Productivity Department Lake Stevens Division
domain: billh@lsid.hp.com M/S 330
phone: (206) 335-2200 8600 Soper Hill Road
fax: (206) 335-2828 Everett, WA 98205-1298
-
gallaher@teleport.com (Ed Gallah
- Member
- Posts: 39
- Joined: Fri Mar 29, 2002 3:39 am
Semantics HELP! Re: "SD is not DiffEq"
>On Tue, 23 Apr 1996, Ed Gallaher wrote (among other things):
>
>[...]
>> I did see the articles in Science. However, these papers described
>> differential equations and not SD models. This is not a trivial
>> difference!
>[...]
In a thoughtful reply George Richardson commented:
>In fact, a system dynamics model *is* a model of the form dX/dt = f(X,p),
>where X is a vector of n states (levels), f is a (usually nonlinear)
>n-dimensional function, and p is a vector of parameters. System dynamics
>models are systems of differential (or, if you prefer, integral)
>equations. John Sterman is right to point out to us system dynamicists
>excellent work in Science in using using such models to address
>significant biological/medical problems, particular when the authors
>translate some of their structural insights into feedback terms. Such
>work is system dynamics.
This topic raises many issues, and I will expand on these in another message.
But first, George, the definitions and semantics contained in this
paragraph are disturbing and confusing to me.
Id prefer to discuss this privately, and then summarize the result to the
group.
I am quite serious about this. We all agree that modeling is useful
because it clarifies and explicates our mental models. My mental model of
"what is system dynamics" does not fit the paragraph above. And perhaps
our collective "marketing" of SD is fuzzy as a result.
Premise:
There are a number of real-world PROBLEMS that involve continuous processes
over time. Many of these involve feedback loops. These processes and
problems existed long before calculus, diff eq, or SD, and are independent
of our ability to understand them or solve them. They just "are".
Various techniques have been developed to study such problems.
If we describe the above problems as "systems", then I suppose any study of
them could be defined as "system dynamics". If so, we need another clear,
unamgigous name for whatever it is that Forrester "invented/developed".
Calculus (Newton and Leibniz), diff eq, control systems engineering, etc.
provide us with a set of tools to study and interpret these problems.
These techniques evolved over several hundred years. The concept of a
limit, and thus calculus itself, was invented largely because it was not
feasible to add up all the little bits and pieces.
Forrester and his colleagues proposed and developed a unified method of
Stock-and-flow diagrams and computer simulation (DYNAMO, STELLA, Powersim,
Vensim, etc). Computers can now add up the bits and pieces for us.
(I am going to state that this latter technique can be conducted without
higher level math background. We can discuss this in another dialog if
there is any disagreement on this point.)
MY PROBLEM: I am looking for a clear, unambiguous NAME for the SPECIFIC
PROCESS which uses stock-and-flow diagrams and closely-linked computer
simulations.
The name which describes the PROCESS must be distinct from name given to
the *set of problems* to which this procedure is applied.
(The railroads defined themselves as being in the railroad business. This
might be considered semantic trivia, until the airlines came along and
pointed out that this was the "transportation" business. The -solution-
(horse vs railroad vs airplane) cannot be equated with the -problem-
(transportation).)
So, I am looking for a clear, unambiguous name.
A fuzzy overlap between systems thinking and system dynamics is NOT OK.
This process does not include hexagons.
This process does not include causal-loop diagrams.
(I cast no aspersions at these latter techniques; they each serve a very
real purpose. But not *this* purpose.)
Should we call this invention/technique "System Dynamics"?
Or "Stock-and-flow Modeling"?
Or "Forrester Modeling"
Or what?
I would suggest "System Dynamics", and I would guess you would too.
But this works if, and ONLY if this term is taken to mean the
invention/technique of stock-and-flow diagrams and computer simulation.
Not if it is meant to describe the *set of problems* for which it is used.
Not if it is confused with Systems Thinking.
Not if it includes causal-loop diagrams.
I am not seeking to discuss the merits of these various techniques or
approaches. Just an unambiguous NAME.
If you still feel that your paragraph above is precisely stated, then can
you provide me with a name that we can agree upon to describe
"stock-and-flow diagrams and the collection of software including
DYNAMO...... Vensim", but NOT including diff eq and other numerical
analysis solutions?
This is not meant to be just argumentative, or a power struggle.
I would like to proceed with a discussion of "whatever it is" vs
"traditional math", but we cant even begin this discussion without a
resolution of the definitions.
Thanks,
Ed
gallaher@teleport.com
P.S. In discussing this several months ago with another colleague (by
phone), he implied that STELLA (i.e. the graphic interface which makes the
process user-friendly, and eliminates the potential diagram-coding
discrepancies of DYNAMO) was a HUGE step forward. But he felt that what
Forrester "invented" was just a way of diagramming and conducting
traditional numerical analysis, i.e. a technical footnote in the calculus
thread.
He (with a very strong math background, by the way), would probably agree
with your paragraph above. We never got this semantics question
resolved. He knew he was right, and knew I was wrong; needles to say
this did not shed too much light on the issue. Writing has advantages over
the phone of course; it allows some contemplation. In addition, I observe
that your style provides more light, less heat than his does, so Im
optimistic that I (we) can achieve some clarity here.
This might shed some further light on where I am coming from on this.
>
>[...]
>> I did see the articles in Science. However, these papers described
>> differential equations and not SD models. This is not a trivial
>> difference!
>[...]
In a thoughtful reply George Richardson commented:
>In fact, a system dynamics model *is* a model of the form dX/dt = f(X,p),
>where X is a vector of n states (levels), f is a (usually nonlinear)
>n-dimensional function, and p is a vector of parameters. System dynamics
>models are systems of differential (or, if you prefer, integral)
>equations. John Sterman is right to point out to us system dynamicists
>excellent work in Science in using using such models to address
>significant biological/medical problems, particular when the authors
>translate some of their structural insights into feedback terms. Such
>work is system dynamics.
This topic raises many issues, and I will expand on these in another message.
But first, George, the definitions and semantics contained in this
paragraph are disturbing and confusing to me.
Id prefer to discuss this privately, and then summarize the result to the
group.
I am quite serious about this. We all agree that modeling is useful
because it clarifies and explicates our mental models. My mental model of
"what is system dynamics" does not fit the paragraph above. And perhaps
our collective "marketing" of SD is fuzzy as a result.
Premise:
There are a number of real-world PROBLEMS that involve continuous processes
over time. Many of these involve feedback loops. These processes and
problems existed long before calculus, diff eq, or SD, and are independent
of our ability to understand them or solve them. They just "are".
Various techniques have been developed to study such problems.
If we describe the above problems as "systems", then I suppose any study of
them could be defined as "system dynamics". If so, we need another clear,
unamgigous name for whatever it is that Forrester "invented/developed".
Calculus (Newton and Leibniz), diff eq, control systems engineering, etc.
provide us with a set of tools to study and interpret these problems.
These techniques evolved over several hundred years. The concept of a
limit, and thus calculus itself, was invented largely because it was not
feasible to add up all the little bits and pieces.
Forrester and his colleagues proposed and developed a unified method of
Stock-and-flow diagrams and computer simulation (DYNAMO, STELLA, Powersim,
Vensim, etc). Computers can now add up the bits and pieces for us.
(I am going to state that this latter technique can be conducted without
higher level math background. We can discuss this in another dialog if
there is any disagreement on this point.)
MY PROBLEM: I am looking for a clear, unambiguous NAME for the SPECIFIC
PROCESS which uses stock-and-flow diagrams and closely-linked computer
simulations.
The name which describes the PROCESS must be distinct from name given to
the *set of problems* to which this procedure is applied.
(The railroads defined themselves as being in the railroad business. This
might be considered semantic trivia, until the airlines came along and
pointed out that this was the "transportation" business. The -solution-
(horse vs railroad vs airplane) cannot be equated with the -problem-
(transportation).)
So, I am looking for a clear, unambiguous name.
A fuzzy overlap between systems thinking and system dynamics is NOT OK.
This process does not include hexagons.
This process does not include causal-loop diagrams.
(I cast no aspersions at these latter techniques; they each serve a very
real purpose. But not *this* purpose.)
Should we call this invention/technique "System Dynamics"?
Or "Stock-and-flow Modeling"?
Or "Forrester Modeling"
Or what?
I would suggest "System Dynamics", and I would guess you would too.
But this works if, and ONLY if this term is taken to mean the
invention/technique of stock-and-flow diagrams and computer simulation.
Not if it is meant to describe the *set of problems* for which it is used.
Not if it is confused with Systems Thinking.
Not if it includes causal-loop diagrams.
I am not seeking to discuss the merits of these various techniques or
approaches. Just an unambiguous NAME.
If you still feel that your paragraph above is precisely stated, then can
you provide me with a name that we can agree upon to describe
"stock-and-flow diagrams and the collection of software including
DYNAMO...... Vensim", but NOT including diff eq and other numerical
analysis solutions?
This is not meant to be just argumentative, or a power struggle.
I would like to proceed with a discussion of "whatever it is" vs
"traditional math", but we cant even begin this discussion without a
resolution of the definitions.
Thanks,
Ed
gallaher@teleport.com
P.S. In discussing this several months ago with another colleague (by
phone), he implied that STELLA (i.e. the graphic interface which makes the
process user-friendly, and eliminates the potential diagram-coding
discrepancies of DYNAMO) was a HUGE step forward. But he felt that what
Forrester "invented" was just a way of diagramming and conducting
traditional numerical analysis, i.e. a technical footnote in the calculus
thread.
He (with a very strong math background, by the way), would probably agree
with your paragraph above. We never got this semantics question
resolved. He knew he was right, and knew I was wrong; needles to say
this did not shed too much light on the issue. Writing has advantages over
the phone of course; it allows some contemplation. In addition, I observe
that your style provides more light, less heat than his does, so Im
optimistic that I (we) can achieve some clarity here.
This might shed some further light on where I am coming from on this.
-
CrbnBlu@aol.com
- Senior Member
- Posts: 67
- Joined: Fri Mar 29, 2002 3:39 am
Semantics HELP! Re: "SD is not DiffEq"
irt: gallaher@teleport.com (Ed Gallaher), Thu, Apr 25, 1996 7:44 PM EST
This is simply marvelous! I wonder what preculuded us from getting here for
so long. Ive read this message several times, now lets see if I have an
appropriate understanding.
The Universe IS! There are different techniques for describing and
understanding how it works. For us to communicate on some meaningful level we
must come to some acceptable agreement as to what labels applied to our
techniques mean, otherwise we just confuse each other, and are often apt to
debate unsubstantiated meaninglessness.
If two different techniques both prove equally adequate for describing the
operation of a system then, althought they remain different techniques, they
are essentially equivalent. I rather relate this to the "universal Turing
machine" being the simplest definition of a computer, and as all computers
can represent the univeral Turing manine they are thus equivalent (more or
less).
I would also relate the discussion to:
All grass is green. This is grass. Therefore it is green.
Which should not be confused with the fallacy:
All grass is green. This is green. Therefore it is grass.
Regarding part of Eds premise:
"There are a number of real-world PROBLEMS that involve continuous processes
over time. Many of these involve feedback loops."
Is there a real-world problem that doesnt involve feedback loops? Even if
one existed, as soon as it was considered, would that create a feedback loop?
Regarding Eds stated "MY PROBLEM," my personal perception which has
developed over time is that that "System Dynamics" is the technique (process)
which uses stock-and-flow diagrams and closely-linked computer simulations to
understand real world problems. I supposed this was why I felt comfortable
writing a paper titled, "System Dynamics: An Operational Guide to the
Universe," presumptuous as it may have been.
As for the comments regarding Systems Thinking, CLDs, etc. I consider them
each to be techniques which provide more and more explicit representations of
what I seek to understand. I seem to repeatedly progress from systematic
thinking, to systems thinking, to CLDs, to System Dynamics (or DEVS -
Discrete Event Simulations, which I perceive as a technique different from
System Dyanmics). As I progress through each technique the understanding (or
the fallacy of my understanding) seems to become more explicit with the more
explicit nature of the technique.
Gene Bellinger
CrbnBlu@aol.com
This is simply marvelous! I wonder what preculuded us from getting here for
so long. Ive read this message several times, now lets see if I have an
appropriate understanding.
The Universe IS! There are different techniques for describing and
understanding how it works. For us to communicate on some meaningful level we
must come to some acceptable agreement as to what labels applied to our
techniques mean, otherwise we just confuse each other, and are often apt to
debate unsubstantiated meaninglessness.
If two different techniques both prove equally adequate for describing the
operation of a system then, althought they remain different techniques, they
are essentially equivalent. I rather relate this to the "universal Turing
machine" being the simplest definition of a computer, and as all computers
can represent the univeral Turing manine they are thus equivalent (more or
less).
I would also relate the discussion to:
All grass is green. This is grass. Therefore it is green.
Which should not be confused with the fallacy:
All grass is green. This is green. Therefore it is grass.
Regarding part of Eds premise:
"There are a number of real-world PROBLEMS that involve continuous processes
over time. Many of these involve feedback loops."
Is there a real-world problem that doesnt involve feedback loops? Even if
one existed, as soon as it was considered, would that create a feedback loop?
Regarding Eds stated "MY PROBLEM," my personal perception which has
developed over time is that that "System Dynamics" is the technique (process)
which uses stock-and-flow diagrams and closely-linked computer simulations to
understand real world problems. I supposed this was why I felt comfortable
writing a paper titled, "System Dynamics: An Operational Guide to the
Universe," presumptuous as it may have been.
As for the comments regarding Systems Thinking, CLDs, etc. I consider them
each to be techniques which provide more and more explicit representations of
what I seek to understand. I seem to repeatedly progress from systematic
thinking, to systems thinking, to CLDs, to System Dynamics (or DEVS -
Discrete Event Simulations, which I perceive as a technique different from
System Dyanmics). As I progress through each technique the understanding (or
the fallacy of my understanding) seems to become more explicit with the more
explicit nature of the technique.
Gene Bellinger
CrbnBlu@aol.com
-
CrbnBlu@aol.com
- Senior Member
- Posts: 67
- Joined: Fri Mar 29, 2002 3:39 am
Semantics HELP! Re: "SD is not DiffEq"
irt: gallaher@teleport.com (Ed Gallaher), Thu, Apr 25, 1996 7:44 PM EST
This is simply marvelous! I wonder what preculuded us from getting here for
so long. Ive read this message several times, now lets see if I have an
appropriate understanding.
The Universe IS! There are different techniques for describing and
understanding how it works. For us to communicate on some meaningful level we
must come to some acceptable agreement as to what labels applied to our
techniques mean, otherwise we just confuse each other, and are often apt to
debate unsubstantiated meaninglessness.
If two different techniques both prove equally adequate for describing the
operation of a system then, althought they remain different techniques, they
are essentially equivalent. I rather relate this to the "universal Turing
machine" being the simplest definition of a computer, and as all computers
can represent the univeral Turing manine they are thus equivalent (more or
less).
I would also relate the discussion to:
All grass is green. This is grass. Therefore it is green.
Which should not be confused with the fallacy:
All grass is green. This is green. Therefore it is grass.
Regarding part of Eds premise:
"There are a number of real-world PROBLEMS that involve continuous processes
over time. Many of these involve feedback loops."
Is there a real-world problem that doesnt involve feedback loops? Even if
one existed, as soon as it was considered, would that create a feedback loop?
Regarding Eds stated "MY PROBLEM," my personal perception which has
developed over time is that that "System Dynamics" is the technique (process)
which uses stock-and-flow diagrams and closely-linked computer simulations to
understand real world problems. I supposed this was why I felt comfortable
writing a paper titled, "System Dynamics: An Operational Guide to the
Universe," presumptuous as it may have been.
As for the comments regarding Systems Thinking, CLDs, etc. I consider them
each to be techniques which provide more and more explicit representations of
what I seek to understand. I seem to repeatedly progress from systematic
thinking, to systems thinking, to CLDs, to System Dynamics (or DEVS -
Discrete Event Simulations, which I perceive as a technique different from
System Dyanmics). As I progress through each technique the understanding (or
the fallacy of my understanding) seems to become more explicit with the more
explicit nature of the technique.
Gene Bellinger
CrbnBlu@aol.com
This is simply marvelous! I wonder what preculuded us from getting here for
so long. Ive read this message several times, now lets see if I have an
appropriate understanding.
The Universe IS! There are different techniques for describing and
understanding how it works. For us to communicate on some meaningful level we
must come to some acceptable agreement as to what labels applied to our
techniques mean, otherwise we just confuse each other, and are often apt to
debate unsubstantiated meaninglessness.
If two different techniques both prove equally adequate for describing the
operation of a system then, althought they remain different techniques, they
are essentially equivalent. I rather relate this to the "universal Turing
machine" being the simplest definition of a computer, and as all computers
can represent the univeral Turing manine they are thus equivalent (more or
less).
I would also relate the discussion to:
All grass is green. This is grass. Therefore it is green.
Which should not be confused with the fallacy:
All grass is green. This is green. Therefore it is grass.
Regarding part of Eds premise:
"There are a number of real-world PROBLEMS that involve continuous processes
over time. Many of these involve feedback loops."
Is there a real-world problem that doesnt involve feedback loops? Even if
one existed, as soon as it was considered, would that create a feedback loop?
Regarding Eds stated "MY PROBLEM," my personal perception which has
developed over time is that that "System Dynamics" is the technique (process)
which uses stock-and-flow diagrams and closely-linked computer simulations to
understand real world problems. I supposed this was why I felt comfortable
writing a paper titled, "System Dynamics: An Operational Guide to the
Universe," presumptuous as it may have been.
As for the comments regarding Systems Thinking, CLDs, etc. I consider them
each to be techniques which provide more and more explicit representations of
what I seek to understand. I seem to repeatedly progress from systematic
thinking, to systems thinking, to CLDs, to System Dynamics (or DEVS -
Discrete Event Simulations, which I perceive as a technique different from
System Dyanmics). As I progress through each technique the understanding (or
the fallacy of my understanding) seems to become more explicit with the more
explicit nature of the technique.
Gene Bellinger
CrbnBlu@aol.com
-
jimhines@interserv.com
- Member
- Posts: 41
- Joined: Fri Mar 29, 2002 3:39 am
Semantics HELP! Re: "SD is not DiffEq"
To: Ed Gallaher, regarding your message #58
Ed,
I think restricting the term "system dynamics" in the way you suggest will cause
a great deal of confusion. As an example, consider causal loop diagrams: Many
people (including me) consider causal loop diagrams as part of system dynamics:
CLDs appear in many of the texts on system dynamics; they are taught as part of
most courses on system dynamics; Vensims underlying graphic metaphore is CLD
(Althgouh it is possible to make these CLDS **look** like stock and flow
diagrams; "flow-pipes", like all of Vensims arrows, actually indicate causal
connections).
I think we should keep "system dynamics" a term that allows growth of the field.
Causal loop diagrams were added later (though not much later) than Industrial
Dynamics; but it seems that CLDs are now part of the fields vocabulary. I
think we should welcome this sort of gradual development.
If we want to refer to something that is part of the field, I think were just
going to have to name it as best we can. Your use of the term "stock-and-flow
diagram", for example, seemed pretty serviceable to me.
Jim Hines
jimhines@interserv.com
Ed,
I think restricting the term "system dynamics" in the way you suggest will cause
a great deal of confusion. As an example, consider causal loop diagrams: Many
people (including me) consider causal loop diagrams as part of system dynamics:
CLDs appear in many of the texts on system dynamics; they are taught as part of
most courses on system dynamics; Vensims underlying graphic metaphore is CLD
(Althgouh it is possible to make these CLDS **look** like stock and flow
diagrams; "flow-pipes", like all of Vensims arrows, actually indicate causal
connections).
I think we should keep "system dynamics" a term that allows growth of the field.
Causal loop diagrams were added later (though not much later) than Industrial
Dynamics; but it seems that CLDs are now part of the fields vocabulary. I
think we should welcome this sort of gradual development.
If we want to refer to something that is part of the field, I think were just
going to have to name it as best we can. Your use of the term "stock-and-flow
diagram", for example, seemed pretty serviceable to me.
Jim Hines
jimhines@interserv.com
-
Jay Forrest
- Junior Member
- Posts: 19
- Joined: Fri Mar 29, 2002 3:39 am
Semantics HELP! Re: "SD is not DiffEq"
Hi Jim!
I am really enjoying the discussion of SD semantics. I am relatively new to
SD (three years and mostly self educated, but with a good modeling
background) so I could be wrong, but it is my impression that until the late
80s, SD was a relatively small, closed group.
With SD growing internationally one would expect the evolutioin of local
deviations from conventional standards. Recent conversations seem to
confirm that SD is being represented as many different things to potential
clients.
I want to thank you, John Sterman, and Ed Gallaher and others for leading
and participating in this discussion. Evolution proceeds by sequential
expansions and contractions. SD has expanded for at least ten years and a
contraction could do much to create greater cohesion in the field and
prepare SD for a more robust and potentially meaningful expansion!
Thanks and Keep Up the Comments!
Jay Forrest
Pteragenesis
Chaos, Complexity, System Dynamics, Studies of the Future
pteragen@neosoft.com
http://www.neosoft.com/~pteragen
I am really enjoying the discussion of SD semantics. I am relatively new to
SD (three years and mostly self educated, but with a good modeling
background) so I could be wrong, but it is my impression that until the late
80s, SD was a relatively small, closed group.
With SD growing internationally one would expect the evolutioin of local
deviations from conventional standards. Recent conversations seem to
confirm that SD is being represented as many different things to potential
clients.
I want to thank you, John Sterman, and Ed Gallaher and others for leading
and participating in this discussion. Evolution proceeds by sequential
expansions and contractions. SD has expanded for at least ten years and a
contraction could do much to create greater cohesion in the field and
prepare SD for a more robust and potentially meaningful expansion!
Thanks and Keep Up the Comments!
Jay Forrest
Pteragenesis
Chaos, Complexity, System Dynamics, Studies of the Future
pteragen@neosoft.com
http://www.neosoft.com/~pteragen
-
gallaher@teleport.com (Ed Gallah
- Member
- Posts: 39
- Joined: Fri Mar 29, 2002 3:39 am
Semantics HELP! Re: "SD is not DiffEq"
>I think restricting the term "system dynamics" in the way you suggest will
>cause a great deal of confusion.
>Jim Hines
Thanks for your reply.
I am not necessarily pushing for a restriction of the term "system
dynamics", but I am looking for A NAME that makes sense.
In a k-12 education setting we need something clear and descriptive. With
as many people in SD from the business arena, it is disconcerting to me
that the "marketing" of systems dynamics has been absolutely abominable.
Ever heard of "confusion in the marketplace"?
I am a longstanding Mac advocate, but in recent years their product line
and corporate policy has become very confusing. Quadras, Performas, Power
PCs, etc, etc. Despite this confusion, they dont hold a candle to "system
dynamics" (or systems thinking, or whatever it is).
I realize we want a growing, lively, dynamic discipline. We do not want to
stagnate with the tools of 1960. However, this does not give us the right
to create so many layers of jargon that we cannot even talk to each other.
And heaven help anyone from the outside who enters our realm!
We just put on a SyM Bowl for high school students last Friday (it went
great, more on this later).
I believe there is a unique body of knowledge contained between the ***** below
*********
Symbols including infinite sources and sinks, amounts, rates, information
links (connectors), input constants, and variable derived from other
components (converters in STELLA). No other symbols! No ovens, conveyer
belts, etc.
Given the above set of symbols, and a valid model structure, we can now run
simulations.
**********
Thats it! This sums up the original concept of SD! It was designed for
continuous system simulation.
This deceptively simple "invention" allows us to model and analyze partial
differential systems, nonlinear systems, feedback and feedforward, etc.
With proper attention to sound modeling practice, this "invention" is
accessible to high school students.
It needs an unambiguous, marketable name!
Im not sure I want to advertise a "High School Stock-and-Flow Diagram
Computer Simulation" contest.
So what do I call it when I am talking to a school board member at the SyM Bowl?
ed
gallaher@teleport.com
>cause a great deal of confusion.
>Jim Hines
Thanks for your reply.
I am not necessarily pushing for a restriction of the term "system
dynamics", but I am looking for A NAME that makes sense.
In a k-12 education setting we need something clear and descriptive. With
as many people in SD from the business arena, it is disconcerting to me
that the "marketing" of systems dynamics has been absolutely abominable.
Ever heard of "confusion in the marketplace"?
I am a longstanding Mac advocate, but in recent years their product line
and corporate policy has become very confusing. Quadras, Performas, Power
PCs, etc, etc. Despite this confusion, they dont hold a candle to "system
dynamics" (or systems thinking, or whatever it is).
I realize we want a growing, lively, dynamic discipline. We do not want to
stagnate with the tools of 1960. However, this does not give us the right
to create so many layers of jargon that we cannot even talk to each other.
And heaven help anyone from the outside who enters our realm!
We just put on a SyM Bowl for high school students last Friday (it went
great, more on this later).
I believe there is a unique body of knowledge contained between the ***** below
*********
Symbols including infinite sources and sinks, amounts, rates, information
links (connectors), input constants, and variable derived from other
components (converters in STELLA). No other symbols! No ovens, conveyer
belts, etc.
Given the above set of symbols, and a valid model structure, we can now run
simulations.
**********
Thats it! This sums up the original concept of SD! It was designed for
continuous system simulation.
This deceptively simple "invention" allows us to model and analyze partial
differential systems, nonlinear systems, feedback and feedforward, etc.
With proper attention to sound modeling practice, this "invention" is
accessible to high school students.
It needs an unambiguous, marketable name!
Im not sure I want to advertise a "High School Stock-and-Flow Diagram
Computer Simulation" contest.
So what do I call it when I am talking to a school board member at the SyM Bowl?
ed
gallaher@teleport.com
-
gallaher@teleport.com (Ed Gallah
- Member
- Posts: 39
- Joined: Fri Mar 29, 2002 3:39 am
Semantics HELP! Re: "SD is not DiffEq"
> Evolution proceeds by sequential
>expansions and contractions. SD has expanded for at least ten years and a
>contraction could do much to create greater cohesion in the field and
>prepare SD for a more robust and potentially meaningful expansion!
I hadnt really thought of it this way, but I believe you are correct.
By working with the CC-STADUS group, including teaching high school
teachers and high school students, I am forced to get things straight in my
own mind, and to simplify. Of course, this is why teaching is so valuable
for all of us. You dont really understand something until you have to
teach it.
Although I had been doing SD (STELLA) modeling for about 6 years, the
confusion/discrepancies etc re System Thinking vs System Dynamics did not
even reach a level of conciousness until I attended the K-12 meeting in
Concord in July 94. Before that it was all the same to me.
I had read The Fifth Discipline, and thought that the archetypes (CLDs)
were begging for stock-and-flow diagrams and computer simulations! At the
time I did not realize that Peter had been a graduate student of JWF, and
that these concepts were firmly grounded in prior SD simulation work.
I understand that Peter is "pulling/pushing" business executives about as
far as possible, and it is unlikely that a Fortune 500 CEO is going to
build stock-and-flow diagrams and run computer simulations. And many other
aspects of organization, management, etc etc play a role in "learning
organizations". S&F modeling and simiulation is not the end-all and
be-all.
That said, I am trying to "contract" and identify a finite piece of this
discipline, which can be clearly identified and delineated, and presented
to high school (and college, and graduate, and medical) students.
We need academicians and scholars (e.g.. this group) who focus on the
discipline of system dynamics per se, just as we need higher mathematical
research. But we also need to identify a subset of clearly defined tools
which are available to the rest of the world, to solve practical problems,
at something less than the Ph.D. level.
In looking at a diffeq text I find multiple examples of dilution problems.
Salt flowing in and out of vats; pesticides flowing in and out of
reservoirs. Theyre all the same problem.
I *KNOW* that if students (sophomore to senior in high school) are
presented with a worksheet for a linear input - exponential output system
(with a year of algebra as a pre-requisite) that they can solve these
problems. Not only that, but with a year or two of experience they can (a)
see the system, (b) formulate the problem, (c) build the diagram, (d)
assign the parameters, (e) state their assumptions, (f) find reference
data, (g) run the simulations, (h) draw conclusions, and (i) describe how
the model can be expanded in future work. This is not theory! They are
doing it.
This is a challenging process, and it does not fit our compartmentalized
view of education. It is also very valuable.
What it doesnt need is interminable discussion and confusion about
definitions and jargon.
Dont get me wrong. I am enjoying this as much as anyone. And I am
learning a tremendous amount, and clarifying many issues that have been
rattling around in my head. And this is the perfect forum for all this.
In fact, there couldnt be a more perfect forum!
But for the sake of teaching applied system dynamics to high school
students, and getting support via school boards, superindents, and parents,
we need SIMPLE, contained, consistent definitions and concepts.
ed gallaher
gallaher@teleport.com
>expansions and contractions. SD has expanded for at least ten years and a
>contraction could do much to create greater cohesion in the field and
>prepare SD for a more robust and potentially meaningful expansion!
I hadnt really thought of it this way, but I believe you are correct.
By working with the CC-STADUS group, including teaching high school
teachers and high school students, I am forced to get things straight in my
own mind, and to simplify. Of course, this is why teaching is so valuable
for all of us. You dont really understand something until you have to
teach it.
Although I had been doing SD (STELLA) modeling for about 6 years, the
confusion/discrepancies etc re System Thinking vs System Dynamics did not
even reach a level of conciousness until I attended the K-12 meeting in
Concord in July 94. Before that it was all the same to me.
I had read The Fifth Discipline, and thought that the archetypes (CLDs)
were begging for stock-and-flow diagrams and computer simulations! At the
time I did not realize that Peter had been a graduate student of JWF, and
that these concepts were firmly grounded in prior SD simulation work.
I understand that Peter is "pulling/pushing" business executives about as
far as possible, and it is unlikely that a Fortune 500 CEO is going to
build stock-and-flow diagrams and run computer simulations. And many other
aspects of organization, management, etc etc play a role in "learning
organizations". S&F modeling and simiulation is not the end-all and
be-all.
That said, I am trying to "contract" and identify a finite piece of this
discipline, which can be clearly identified and delineated, and presented
to high school (and college, and graduate, and medical) students.
We need academicians and scholars (e.g.. this group) who focus on the
discipline of system dynamics per se, just as we need higher mathematical
research. But we also need to identify a subset of clearly defined tools
which are available to the rest of the world, to solve practical problems,
at something less than the Ph.D. level.
In looking at a diffeq text I find multiple examples of dilution problems.
Salt flowing in and out of vats; pesticides flowing in and out of
reservoirs. Theyre all the same problem.
I *KNOW* that if students (sophomore to senior in high school) are
presented with a worksheet for a linear input - exponential output system
(with a year of algebra as a pre-requisite) that they can solve these
problems. Not only that, but with a year or two of experience they can (a)
see the system, (b) formulate the problem, (c) build the diagram, (d)
assign the parameters, (e) state their assumptions, (f) find reference
data, (g) run the simulations, (h) draw conclusions, and (i) describe how
the model can be expanded in future work. This is not theory! They are
doing it.
This is a challenging process, and it does not fit our compartmentalized
view of education. It is also very valuable.
What it doesnt need is interminable discussion and confusion about
definitions and jargon.
Dont get me wrong. I am enjoying this as much as anyone. And I am
learning a tremendous amount, and clarifying many issues that have been
rattling around in my head. And this is the perfect forum for all this.
In fact, there couldnt be a more perfect forum!
But for the sake of teaching applied system dynamics to high school
students, and getting support via school boards, superindents, and parents,
we need SIMPLE, contained, consistent definitions and concepts.
ed gallaher
gallaher@teleport.com
-
CrbnBlu@aol.com
- Senior Member
- Posts: 67
- Joined: Fri Mar 29, 2002 3:39 am
Semantics HELP! Re: "SD is not DiffEq"
irt: gallaher@teleport.com (Ed Gallaher), Mon, Apr 29, 1996 6:32 PM EST
Ed, regarding the name youre looking for, could it be the question is being
posed to the wrong audience? Maybe it would be good to ask the students what
to call it. I repeatedly find that students are often the best teachers --
when we are insightful enought to pay attention to them that is!
Gene Bellinger
CrbnBlu@aol.com
PS When I forget that I am a student I seem to enter periods during which
not much learning happens. There are also times when searching results in no
answers at all and it is better just to be still and allow the answer to find
you.
Ed, regarding the name youre looking for, could it be the question is being
posed to the wrong audience? Maybe it would be good to ask the students what
to call it. I repeatedly find that students are often the best teachers --
when we are insightful enought to pay attention to them that is!
Gene Bellinger
CrbnBlu@aol.com
PS When I forget that I am a student I seem to enter periods during which
not much learning happens. There are also times when searching results in no
answers at all and it is better just to be still and allow the answer to find
you.
-
Jim Hines
- Senior Member
- Posts: 80
- Joined: Fri Mar 29, 2002 3:39 am
Semantics HELP! Re: "SD is not DiffEq"
Jay,
I think you are right that SD has grown sometimes faster and sometimes
slower. And my perception is also that the last decade has seen a
rapid increase in interest. (As good SDers, of course its hard for us
to say whether this is due to an increase in the **rate** of expansion
or just an increase in the **base** on which the rate acts).
You also mention that with the field growing faster we should expect the
evolution of "local devations from conventional standards". To some
extent, I think there always have been local differences (for example,
Europeans have seemed different from Americans to me; and within the
U.S., the Rockefeller folks have somewhat different concerns from the
MIT folks; etc.).
Some evolutionary divergence is healthy. Having people exploring
different aspects of the field is a very good thing. Still, I think its
valuable to continue "genetic" exchanges between groups -- its a bit too
early for true speciation.
The necessary cohesion can be had in different ways. A contraction as
you suggest could perhaps do it. Personally, I hope that a contraction
of the field is not in the offing. I think that efforts such as this
email forum represents a better way to foster exchange and cohesion.
Bob Eberlein of Ventana Systems, who has organized and continues to
monitor this forum, deserves a great deal of appreciation.
Another good avenue for exchange and cohesion are the conferences.
There are two in Boston this summer. I hope that many of the people on
the email list might meet face to face this summer!
Regards,
Jim Hines
I think you are right that SD has grown sometimes faster and sometimes
slower. And my perception is also that the last decade has seen a
rapid increase in interest. (As good SDers, of course its hard for us
to say whether this is due to an increase in the **rate** of expansion
or just an increase in the **base** on which the rate acts).
You also mention that with the field growing faster we should expect the
evolution of "local devations from conventional standards". To some
extent, I think there always have been local differences (for example,
Europeans have seemed different from Americans to me; and within the
U.S., the Rockefeller folks have somewhat different concerns from the
MIT folks; etc.).
Some evolutionary divergence is healthy. Having people exploring
different aspects of the field is a very good thing. Still, I think its
valuable to continue "genetic" exchanges between groups -- its a bit too
early for true speciation.
The necessary cohesion can be had in different ways. A contraction as
you suggest could perhaps do it. Personally, I hope that a contraction
of the field is not in the offing. I think that efforts such as this
email forum represents a better way to foster exchange and cohesion.
Bob Eberlein of Ventana Systems, who has organized and continues to
monitor this forum, deserves a great deal of appreciation.
Another good avenue for exchange and cohesion are the conferences.
There are two in Boston this summer. I hope that many of the people on
the email list might meet face to face this summer!
Regards,
Jim Hines
-
Jim Hines
- Senior Member
- Posts: 80
- Joined: Fri Mar 29, 2002 3:39 am
Semantics HELP! Re: "SD is not DiffEq"
Ed,
I agree that "High School Stock-and-Flow Diagram Computer Simulation"
contest doesnt have much marketing flair. (Incidentally, what little I
know about your SyM Bowl sounds terrific and apparently its also good
marketing!).
How did you describe SyM Bowl? I forget how I first heard about it, but
I was quite clear (I think) on what kind of models you were looking for.
Jim Hines
jimhines@interserv.com
I agree that "High School Stock-and-Flow Diagram Computer Simulation"
contest doesnt have much marketing flair. (Incidentally, what little I
know about your SyM Bowl sounds terrific and apparently its also good
marketing!).
How did you describe SyM Bowl? I forget how I first heard about it, but
I was quite clear (I think) on what kind of models you were looking for.
Jim Hines
jimhines@interserv.com
-
gallaher@teleport.com (Ed Gallah
- Member
- Posts: 39
- Joined: Fri Mar 29, 2002 3:39 am
Semantics HELP! Re: "SD is not DiffEq"
>irt: gallaher@teleport.com (Ed Gallaher), Mon, Apr 29, 1996 6:32 PM EST
>When I forget that I am a student I seem to enter periods during which
>not much learning happens. There are also times when searching results in no
>answers at all and it is better just to be still and allow the answer to find
>you.
Absolutely true! And the answer may very well have found me. See message
from John Edwards, and my reply.
Comments anywone?
ed
gallaher@teleport.com
>When I forget that I am a student I seem to enter periods during which
>not much learning happens. There are also times when searching results in no
>answers at all and it is better just to be still and allow the answer to find
>you.
Absolutely true! And the answer may very well have found me. See message
from John Edwards, and my reply.
Comments anywone?
ed
gallaher@teleport.com
-
gallaher@teleport.com (Ed Gallah
- Member
- Posts: 39
- Joined: Fri Mar 29, 2002 3:39 am
Semantics HELP! Re: "SD is not DiffEq"
>Jim Hines said to Jay Forrest:
>
>I think you are right that SD has grown sometimes faster and sometimes
>slower. And my perception is also that the last decade has seen a
>rapid increase in interest. (As good SDers, of course its hard for us
>to say whether this is due to an increase in the **rate** of expansion
>or just an increase in the **base** on which the rate acts).
touche
>The necessary cohesion can be had in different ways. A contraction as
>you suggest could perhaps do it. Personally, I hope that a contraction
>of the field is not in the offing.
Im not sure that contraction is desirable, but perhaps some
consolidation. Im finding many concepts being clarified by these
discussions. Of course Im new to this community. Im not new to DYNAMO
or STELLA, but I am new to this level of discourse.
>Bob Eberlein of Ventana Systems, who has organized and continues to
>monitor this forum, deserves a great deal of appreciation.
Hear! Hear!
>Another good avenue for exchange and cohesion are the conferences.
>There are two in Boston this summer. I hope that many of the people on
>the email list might meet face to face this summer!
I hope so, too. Ill be there.
Ed
gallaher@teleport.com
>
>I think you are right that SD has grown sometimes faster and sometimes
>slower. And my perception is also that the last decade has seen a
>rapid increase in interest. (As good SDers, of course its hard for us
>to say whether this is due to an increase in the **rate** of expansion
>or just an increase in the **base** on which the rate acts).
touche
>The necessary cohesion can be had in different ways. A contraction as
>you suggest could perhaps do it. Personally, I hope that a contraction
>of the field is not in the offing.
Im not sure that contraction is desirable, but perhaps some
consolidation. Im finding many concepts being clarified by these
discussions. Of course Im new to this community. Im not new to DYNAMO
or STELLA, but I am new to this level of discourse.
>Bob Eberlein of Ventana Systems, who has organized and continues to
>monitor this forum, deserves a great deal of appreciation.
Hear! Hear!
>Another good avenue for exchange and cohesion are the conferences.
>There are two in Boston this summer. I hope that many of the people on
>the email list might meet face to face this summer!
I hope so, too. Ill be there.
Ed
gallaher@teleport.com
-
Jay Forrest
- Junior Member
- Posts: 19
- Joined: Fri Mar 29, 2002 3:39 am
Semantics HELP! Re: "SD is not DiffEq"
Hi Jim!
>Some evolutionary divergence is healthy. Having people exploring
>different aspects of the field is a very good thing. Still, I think its
>valuable to continue "genetic" exchanges between groups -- its a bit too
>early for true speciation.
Fully Agreed!
>The necessary cohesion can be had in different ways. A contraction as
>you suggest could perhaps do it. Personally, I hope that a contraction
>of the field is not in the offing.
Ack! Not what I meant. There are two primary facets of contractoin. 1)
The contraction is a pulling in of the diverse ideas, and shaking the chaff
out and to an extent redefining the field as the best is kept. 2)
Contraction in the form of establishing a tighter, more cohesive
understanding of the topic. I did not mean a contraction of popularity.
It appears to me that the "boom" in popularity since Senges book has
resulted in a lot of different descriptions of the field - some of which are
somewhat in contradiction. As the field becomes "muddy" from confusion
resulting from muddled connotations (very likely the product of growth), the
field can become a hard sell, especially to outsiders (like businessmen).
The contraction I see happening here is that the debate is helping a lot of
us lurkers (like me) who are relatively self-trained hone our understaning
of the field and to move toward a "core" understanding. That contraction
creates a more cohesive field. That can facilitate sales to outsiders
because we collectively are more consistent. This kind of contraction is
often necessary after a period of growth before the field can grow to some
higher level.
In somewhat different words, diversity is important. It is where new ideas
and growth of the field come from. But as the ideas proliferate, the field
becomes fuzzy and less tangible. The contraction tightens the "definition"
(hopefully by getting rid of the "bad" ideas and keeping the "good" ideas)
and prepares the field for another burst of growth. Hope that helps!
>Another good avenue for exchange and cohesion are the conferences.
>There are two in Boston this summer. I hope that many of the people on
>the email list might meet face to face this summer!
I wish I could go. Just no way! Alas! Oh well! Maybe next year!
Jay
Pteragenesis
Chaos, Complexity, System Dynamics, Studies of the Future
pteragen@neosoft.com
http://www.neosoft.com/~pteragen
>Some evolutionary divergence is healthy. Having people exploring
>different aspects of the field is a very good thing. Still, I think its
>valuable to continue "genetic" exchanges between groups -- its a bit too
>early for true speciation.
Fully Agreed!
>The necessary cohesion can be had in different ways. A contraction as
>you suggest could perhaps do it. Personally, I hope that a contraction
>of the field is not in the offing.
Ack! Not what I meant. There are two primary facets of contractoin. 1)
The contraction is a pulling in of the diverse ideas, and shaking the chaff
out and to an extent redefining the field as the best is kept. 2)
Contraction in the form of establishing a tighter, more cohesive
understanding of the topic. I did not mean a contraction of popularity.
It appears to me that the "boom" in popularity since Senges book has
resulted in a lot of different descriptions of the field - some of which are
somewhat in contradiction. As the field becomes "muddy" from confusion
resulting from muddled connotations (very likely the product of growth), the
field can become a hard sell, especially to outsiders (like businessmen).
The contraction I see happening here is that the debate is helping a lot of
us lurkers (like me) who are relatively self-trained hone our understaning
of the field and to move toward a "core" understanding. That contraction
creates a more cohesive field. That can facilitate sales to outsiders
because we collectively are more consistent. This kind of contraction is
often necessary after a period of growth before the field can grow to some
higher level.
In somewhat different words, diversity is important. It is where new ideas
and growth of the field come from. But as the ideas proliferate, the field
becomes fuzzy and less tangible. The contraction tightens the "definition"
(hopefully by getting rid of the "bad" ideas and keeping the "good" ideas)
and prepares the field for another burst of growth. Hope that helps!
>Another good avenue for exchange and cohesion are the conferences.
>There are two in Boston this summer. I hope that many of the people on
>the email list might meet face to face this summer!
I wish I could go. Just no way! Alas! Oh well! Maybe next year!
Jay
Pteragenesis
Chaos, Complexity, System Dynamics, Studies of the Future
pteragen@neosoft.com
http://www.neosoft.com/~pteragen