>
> The end result being that I am now quite comfortable modeling and simulating
> ST diagrams, and I dont even miss the Stock-Flow diagrams. Now I no longer
> need two different pictures.
>
> Your first thought about this is probably related to how one tells the
> difference between Stocks, Flows, Converters, and Information Flows. I have
> found that color coding the components of the model works just fine.
>
Actually, one can just "control click" on each of the implicit levels in
your "ST" diagram (causal-loop diagram?) and set the surround shape to be
a "box." Bingo: you have identified the stocks, and the flows into and
out of them can be named to show up nicely as flows, and/or you can
"control click" on the arrow heads of flows and put +s or -s signs on
all the flows. No color is necessary to distinguish stocks and flows and
others, which is nice for printing or publication.
...George
G.P.Richardson@Albany.edu
Heresy 101
Heresy 101
Regarding CLD vs. S&F diagrams:
The two kinds of diagrams emphasize different things. Causal loops
emphasize feedback; stock and flows emphasize, well, stocks and flows.
Both feedback and the process of integration create dynamics (i.e.
change the shape of an input); and consequently both views are
important.
I think that most good SDers, when they start with a stock and flow
diagram most often have in the back of their minds the loops. And, when
they start with a loop diagram, they have in the back of their mind the
stocks and flows.
Id like to think that a good system dynamics person is technically able
to use either form at the initial stages of a project and chooses one
form over the other based not only on personal preference but also on
the needs of the group he is working with and, importantly, on what is
salient in the problem being addressed.
Regards,
Jim Hines
jimhines@interserv.com
The two kinds of diagrams emphasize different things. Causal loops
emphasize feedback; stock and flows emphasize, well, stocks and flows.
Both feedback and the process of integration create dynamics (i.e.
change the shape of an input); and consequently both views are
important.
I think that most good SDers, when they start with a stock and flow
diagram most often have in the back of their minds the loops. And, when
they start with a loop diagram, they have in the back of their mind the
stocks and flows.
Id like to think that a good system dynamics person is technically able
to use either form at the initial stages of a project and chooses one
form over the other based not only on personal preference but also on
the needs of the group he is working with and, importantly, on what is
salient in the problem being addressed.
Regards,
Jim Hines
jimhines@interserv.com
-
CrbnBlu@aol.com
- Senior Member
- Posts: 67
- Joined: Fri Mar 29, 2002 3:39 am
Heresy 101
The following is a thought to share for you comment.
Over the past two weeks Ive been working the Vensim PLE and in the process
something quite unexpected has developed.
In constructing models I almost always create ST diagrams as sort of a road
map as to just what the model is going to be. These are done in some other
drawing package. Once the ST diagram is done I then implement it as a
Stock-Flow model in a simulation package. It has always bothered me that I
had to use two packages to do this because Im basically lazy.
As I started using Vensim PLE if was pleased that I could build the ST
diagrams in the same software package I would build the model in. After
building the first couple ST diagrams and then destroying them in the process
of converting the ST diagram to a Stock-Flow diagram I commented to Bob
Eberline how frustrating it was destroying the initial ST diagram. Bob
commented that the picture was sort of irrelevant and what really mattered
was the formulas contained in the elements of the diagram. It took a couple
days for this to really sink in, and then about two hours to reorient my mind
as to the implications of this.
The end result being that I am now quite comfortable modeling and simulating
ST diagrams, and I dont even miss the Stock-Flow diagrams. Now I no longer
need two different pictures.
Your first thought about this is probably related to how one tells the
difference between Stocks, Flows, Converters, and Information Flows. I have
found that color coding the components of the model works just fine.
Thoughts?
Gene Bellinger
CrbnBlu@aol.com
Over the past two weeks Ive been working the Vensim PLE and in the process
something quite unexpected has developed.
In constructing models I almost always create ST diagrams as sort of a road
map as to just what the model is going to be. These are done in some other
drawing package. Once the ST diagram is done I then implement it as a
Stock-Flow model in a simulation package. It has always bothered me that I
had to use two packages to do this because Im basically lazy.
As I started using Vensim PLE if was pleased that I could build the ST
diagrams in the same software package I would build the model in. After
building the first couple ST diagrams and then destroying them in the process
of converting the ST diagram to a Stock-Flow diagram I commented to Bob
Eberline how frustrating it was destroying the initial ST diagram. Bob
commented that the picture was sort of irrelevant and what really mattered
was the formulas contained in the elements of the diagram. It took a couple
days for this to really sink in, and then about two hours to reorient my mind
as to the implications of this.
The end result being that I am now quite comfortable modeling and simulating
ST diagrams, and I dont even miss the Stock-Flow diagrams. Now I no longer
need two different pictures.
Your first thought about this is probably related to how one tells the
difference between Stocks, Flows, Converters, and Information Flows. I have
found that color coding the components of the model works just fine.
Thoughts?
Gene Bellinger
CrbnBlu@aol.com
-
Stephen Wehrenberg
- Member
- Posts: 29
- Joined: Fri Mar 29, 2002 3:39 am
Heresy 101
CrbnBlu@aol.com (aka Gene Bellinger) wrote:
snip
> As I started using Vensim PLE if was pleased that I could build the ST
> diagrams in the same software package I would build the model in. After
> building the first couple ST diagrams and then destroying them in the process
> of converting the ST diagram to a Stock-Flow diagram I commented to Bob
> Eberline how frustrating it was destroying the initial ST diagram. Bob
> commented that the picture was sort of irrelevant and what really mattered
> was the formulas contained in the elements of the diagram. It took a couple
> days for this to really sink in, and then about two hours to reorient my mind
> as to the implications of this.
Gene: Youve stepped into the middle of what seems (IMHO) to be an
almost-religious controversy. One school of thought extolls the virtues of the
causal loop diagram as the entre to thinking systemically about a problem. The
other decries the use of the CLD until AFTER you have built the stock and flow
model ... then the CLD becomes a useful way to summarize the system in question.
Personally I find myself squarely in both camps ... the argument almost sounds
like a MAC vs PC or WordPerfect vs Word argument (or Wordstar vs EMACS, depending
on where in the baby-boom you find yourself) -- whatever you grew up on is the
best way to look at the world. In some ways, the discussion about the merits of
Vensim vs IThink vs PowerSim is right here. I grew up in a STELLA/IThink
environment, so the S/F approach is the best FOR ME IN MOST CIRCUMSTANCES. But
this seems more than just a matter of preference ... Barry Richmond, for example,
in a very insightful paper on the HPS web site, suggests that using the CLD as an
exploration tool actually works AGAINST developing a profound understanding of the
system in question, and feels that the use of the archetype by those not already
versed in ST/SD is dangerous and probably counterproductive.
I was in Boston last week and addressed this question to just about everyone who
would stop to listen. Richmond made a strong case for S/F first, CLD last. John
Sterman is decidedly on the same side. Forrester certainly didnt start with the
CLD, for reasons related to the science. On the other hand, Senge and most of the
folks at Innovation Associates (and MIT for that matter) see power in the CLD as
both simple, and explanatory --- a good introduction to systems thinking concepts.
I have argued against the casual use of the CLD because it is inherently
undisciplined (as you suggest in your last paragraph) ... it it too easy to create
stocks that seem to be affected by stocks ... a no no in Forresters eyes.
I take issue with Bob Eberleins comment that "... the picture was sort of
irrelevant and what really mattered was the formulas contained in the elements of
the diagram." The picture DOES matter if you are trying to help others use ST and
SD tools to solve problems in situ. A modeler sitting on the other side of the
transom can use any method he or she is comfortable with ... but the objective
(and reality) will be a product, not learning. If the objective is learning, form
takes on great importance. I took this up with him in Boston, and further
critized what I consider to be the worst of all worlds ... mixing the CLD and S/F
forms in the same diagram. Thats just too much for me.
Personally, I find the CLD to be easier for people to grasp, but also much less
effective in promoting structural learning. Stocks and flows contain a much
needed discipline --- what are nouns, what are verbs, what things are conserved,
what things are transformed, etc. Once people get really good at it, anything
will do. The question in my mind becomes "what works best given my current
objective." If it looks like we will be going to modeling, Id rather start with
stocks and flows. If it seems as if we will be able to gain the necessary insight
without resorting to modeling, the CLD is easier. Trick is to know in advance, I
guess.
> The end result being that I am now quite comfortable modeling and simulating
> ST diagrams, and I dont even miss the Stock-Flow diagrams. Now I no longer
> need two different pictures.
Thats cause you already understand what youre doing. A court case in England
put the game of darts on trial ... if it was a game of chance, gambling about the
outcomes would be illegal ... if it was a game of skill, gambling would be ok.
The counsel called one witness, who picked up three twenty-penny nails and threw
three bulls. Luck or skill? Moral is, when youre good at it, you can use any
tool to get the end you want. Its novices who buy the $500 titanium adjustable
weight and balance darts.
> Your first thought about this is probably related to how one tells the
> difference between Stocks, Flows, Converters, and Information Flows. I have
> found that color coding the components of the model works just fine.
This is how YOU impose the discipline of S/F diagrams to the CLD. I rest my case.
Hope this didnt sound too pedagogical ... but its an area Im very concerned
about. You only get to introduce systems thinking once in an organization
(innocculation phenomenon), so you have to choose the right track ... thats where
I am right now.
Steve
--
Stephen B. Wehrenberg, Ph.D.
Chief, Forecasts and Systems, US Coast Guard;
Administrative Sciences Program, The George Washington University;
wstephen@erols.com
snip
> As I started using Vensim PLE if was pleased that I could build the ST
> diagrams in the same software package I would build the model in. After
> building the first couple ST diagrams and then destroying them in the process
> of converting the ST diagram to a Stock-Flow diagram I commented to Bob
> Eberline how frustrating it was destroying the initial ST diagram. Bob
> commented that the picture was sort of irrelevant and what really mattered
> was the formulas contained in the elements of the diagram. It took a couple
> days for this to really sink in, and then about two hours to reorient my mind
> as to the implications of this.
Gene: Youve stepped into the middle of what seems (IMHO) to be an
almost-religious controversy. One school of thought extolls the virtues of the
causal loop diagram as the entre to thinking systemically about a problem. The
other decries the use of the CLD until AFTER you have built the stock and flow
model ... then the CLD becomes a useful way to summarize the system in question.
Personally I find myself squarely in both camps ... the argument almost sounds
like a MAC vs PC or WordPerfect vs Word argument (or Wordstar vs EMACS, depending
on where in the baby-boom you find yourself) -- whatever you grew up on is the
best way to look at the world. In some ways, the discussion about the merits of
Vensim vs IThink vs PowerSim is right here. I grew up in a STELLA/IThink
environment, so the S/F approach is the best FOR ME IN MOST CIRCUMSTANCES. But
this seems more than just a matter of preference ... Barry Richmond, for example,
in a very insightful paper on the HPS web site, suggests that using the CLD as an
exploration tool actually works AGAINST developing a profound understanding of the
system in question, and feels that the use of the archetype by those not already
versed in ST/SD is dangerous and probably counterproductive.
I was in Boston last week and addressed this question to just about everyone who
would stop to listen. Richmond made a strong case for S/F first, CLD last. John
Sterman is decidedly on the same side. Forrester certainly didnt start with the
CLD, for reasons related to the science. On the other hand, Senge and most of the
folks at Innovation Associates (and MIT for that matter) see power in the CLD as
both simple, and explanatory --- a good introduction to systems thinking concepts.
I have argued against the casual use of the CLD because it is inherently
undisciplined (as you suggest in your last paragraph) ... it it too easy to create
stocks that seem to be affected by stocks ... a no no in Forresters eyes.
I take issue with Bob Eberleins comment that "... the picture was sort of
irrelevant and what really mattered was the formulas contained in the elements of
the diagram." The picture DOES matter if you are trying to help others use ST and
SD tools to solve problems in situ. A modeler sitting on the other side of the
transom can use any method he or she is comfortable with ... but the objective
(and reality) will be a product, not learning. If the objective is learning, form
takes on great importance. I took this up with him in Boston, and further
critized what I consider to be the worst of all worlds ... mixing the CLD and S/F
forms in the same diagram. Thats just too much for me.
Personally, I find the CLD to be easier for people to grasp, but also much less
effective in promoting structural learning. Stocks and flows contain a much
needed discipline --- what are nouns, what are verbs, what things are conserved,
what things are transformed, etc. Once people get really good at it, anything
will do. The question in my mind becomes "what works best given my current
objective." If it looks like we will be going to modeling, Id rather start with
stocks and flows. If it seems as if we will be able to gain the necessary insight
without resorting to modeling, the CLD is easier. Trick is to know in advance, I
guess.
> The end result being that I am now quite comfortable modeling and simulating
> ST diagrams, and I dont even miss the Stock-Flow diagrams. Now I no longer
> need two different pictures.
Thats cause you already understand what youre doing. A court case in England
put the game of darts on trial ... if it was a game of chance, gambling about the
outcomes would be illegal ... if it was a game of skill, gambling would be ok.
The counsel called one witness, who picked up three twenty-penny nails and threw
three bulls. Luck or skill? Moral is, when youre good at it, you can use any
tool to get the end you want. Its novices who buy the $500 titanium adjustable
weight and balance darts.
> Your first thought about this is probably related to how one tells the
> difference between Stocks, Flows, Converters, and Information Flows. I have
> found that color coding the components of the model works just fine.
This is how YOU impose the discipline of S/F diagrams to the CLD. I rest my case.
Hope this didnt sound too pedagogical ... but its an area Im very concerned
about. You only get to introduce systems thinking once in an organization
(innocculation phenomenon), so you have to choose the right track ... thats where
I am right now.
Steve
--
Stephen B. Wehrenberg, Ph.D.
Chief, Forecasts and Systems, US Coast Guard;
Administrative Sciences Program, The George Washington University;
wstephen@erols.com
-
CrbnBlu@aol.com
- Senior Member
- Posts: 67
- Joined: Fri Mar 29, 2002 3:39 am
Heresy 101
Stephen,
I rather figured I was about to "step in it" big time with this one and
thought it would be rather interesting to read the responses that resulted.
My response is mostly:
"We choose what we believe and then we believe what we choose."
We repeatedly do ourselves a disservice with our defensiveness. In the veign
of Willima James and Thomas Kuhn, we spend enormous amounts of time defending
our ideas and theories as opposed to attmepting to disprove them, which would
often be much more appropriate.
"To prove all crows are not black I dont have to count all the crows. I only
need to find one white one."
I have a copy of Barrys paper and found it most informative; mabye not
informative enought if I stand in disagreement with it. Maybe Ill go back
and read it again.
I would rather you not take issue with Bob Eberleins comment as I think what
you have issue with is my interpretation and rephrasing of his comment. I
dont think it was really his intention to imply the picutre was irrelevant,
for there is meaning in the picture. I believe the implication was that the
formulas and connections dictated how the simulation worked, not the shape of
the pieces of the picture.
Your comment about simulating CLDs making sense to me because I understand
what Im doing is rather appropriate. I have fallen into a trap of my own
creation, being that I have lost sight of what it was like not to know as
much as I do now. Which I really dont claim is that much, which is why I
keep questioning things.
I also connect will with your comment about me creating my own S/F diagrams
from the CLDs via color coding..., yet the color coding seems to take me less
time than building a new diagram.
thanks for your comments,
Gene Bellinger
CrbnBlu@aol.com
I rather figured I was about to "step in it" big time with this one and
thought it would be rather interesting to read the responses that resulted.
My response is mostly:
"We choose what we believe and then we believe what we choose."
We repeatedly do ourselves a disservice with our defensiveness. In the veign
of Willima James and Thomas Kuhn, we spend enormous amounts of time defending
our ideas and theories as opposed to attmepting to disprove them, which would
often be much more appropriate.
"To prove all crows are not black I dont have to count all the crows. I only
need to find one white one."
I have a copy of Barrys paper and found it most informative; mabye not
informative enought if I stand in disagreement with it. Maybe Ill go back
and read it again.
I would rather you not take issue with Bob Eberleins comment as I think what
you have issue with is my interpretation and rephrasing of his comment. I
dont think it was really his intention to imply the picutre was irrelevant,
for there is meaning in the picture. I believe the implication was that the
formulas and connections dictated how the simulation worked, not the shape of
the pieces of the picture.
Your comment about simulating CLDs making sense to me because I understand
what Im doing is rather appropriate. I have fallen into a trap of my own
creation, being that I have lost sight of what it was like not to know as
much as I do now. Which I really dont claim is that much, which is why I
keep questioning things.
I also connect will with your comment about me creating my own S/F diagrams
from the CLDs via color coding..., yet the color coding seems to take me less
time than building a new diagram.
thanks for your comments,
Gene Bellinger
CrbnBlu@aol.com
-
PKucera@aol.com
- Junior Member
- Posts: 8
- Joined: Fri Mar 29, 2002 3:39 am
Heresy 101
Gene:
The reality of systems is that everything is connected to everything else.
When building CLDs, there is a tendency among many folks to not pay enough
attention to the boundaries of the system under examination. CLDs may
quickly turn into spaghetti; the ESSENCE of the process/system is often loss
in the mess.
Beginning with a stock/flow representation: 1) demands of the
mapper/modeler consideration of explicit boundaries of the system under
consideration (these boundaries indicated by the "clouds" in the map/model);
and 2) makes explicit the distinction between actions (flows) and conditions
(stocks), a ditinction that is lost in CLDs and that is useful in
understanding system structure.
I therefore am in the camp that believes that CLDs are most effective when
used to summarize a stock-flow map/model.
Paul Kucera
PKucera@aol.com
The reality of systems is that everything is connected to everything else.
When building CLDs, there is a tendency among many folks to not pay enough
attention to the boundaries of the system under examination. CLDs may
quickly turn into spaghetti; the ESSENCE of the process/system is often loss
in the mess.
Beginning with a stock/flow representation: 1) demands of the
mapper/modeler consideration of explicit boundaries of the system under
consideration (these boundaries indicated by the "clouds" in the map/model);
and 2) makes explicit the distinction between actions (flows) and conditions
(stocks), a ditinction that is lost in CLDs and that is useful in
understanding system structure.
I therefore am in the camp that believes that CLDs are most effective when
used to summarize a stock-flow map/model.
Paul Kucera
PKucera@aol.com
-
CrbnBlu@aol.com
- Senior Member
- Posts: 67
- Joined: Fri Mar 29, 2002 3:39 am
Heresy 101
irt: PKucera@aol.com, Thu, Jun 20, 1996 10:46 PM EST
Paul,
I hear you, I understand, and I agree.
And I would ask, "How would you go about proving that your perspective is
incorrect? Have you tried?"
Gene...
CrbnBlu@aol.com
Paul,
I hear you, I understand, and I agree.
And I would ask, "How would you go about proving that your perspective is
incorrect? Have you tried?"
Gene...
CrbnBlu@aol.com
-
Stephen Wehrenberg
- Member
- Posts: 29
- Joined: Fri Mar 29, 2002 3:39 am
Heresy 101
Gene,
"We choose what we believe and then we believe what we choose."
The circle of inference, eh? Senge likes to depict it as a ladder, but its
clearly a circle.
Your original comments have certainly started a conversation, if nothing else. As
A. Einstein said, "The important thing is not to stop questioning."
Are you going to Boston in July for the Systems Dynamics Conference, by any
chance?
Steve
--
Stephen B. Wehrenberg
Chief, Forecasts and Systems, US Coast Guard;
Administrative Sciences, The George Washington University
wstephen@erols.com
"Life is a jam session."
"We choose what we believe and then we believe what we choose."
The circle of inference, eh? Senge likes to depict it as a ladder, but its
clearly a circle.
Your original comments have certainly started a conversation, if nothing else. As
A. Einstein said, "The important thing is not to stop questioning."
Are you going to Boston in July for the Systems Dynamics Conference, by any
chance?
Steve
--
Stephen B. Wehrenberg
Chief, Forecasts and Systems, US Coast Guard;
Administrative Sciences, The George Washington University
wstephen@erols.com
"Life is a jam session."
-
CrbnBlu@aol.com
- Senior Member
- Posts: 67
- Joined: Fri Mar 29, 2002 3:39 am
Heresy 101
irt: Date: wstephen@erols.com (Stephen Wehrenberg), Sat, Jun 22, 1996 5:25 AM
EST
In response to "We choose what we believe and then we believe what we
choose." you commented, "The circle of inference, eh? Senge likes to depict
it as a ladder, but its clearly a circle."
Ive been toying with this some and have come up with a "reality short
circuit" which Im not sure Ive got all sorted out yet. If you would care to
take a look at:
http://www.radix.net/~crbnblu/main/person/loi/loi.html
maybe you can offer some comments that will help me sor this out some more.
As for the SD conference in Boston in July, it was on the schedule, yet the
current project in KC is in a phase were I think it best I not be away for a
week.
be well all,
Gene Bellinger
CrbnBlu@aol.com
EST
In response to "We choose what we believe and then we believe what we
choose." you commented, "The circle of inference, eh? Senge likes to depict
it as a ladder, but its clearly a circle."
Ive been toying with this some and have come up with a "reality short
circuit" which Im not sure Ive got all sorted out yet. If you would care to
take a look at:
http://www.radix.net/~crbnblu/main/person/loi/loi.html
maybe you can offer some comments that will help me sor this out some more.
As for the SD conference in Boston in July, it was on the schedule, yet the
current project in KC is in a phase were I think it best I not be away for a
week.
be well all,
Gene Bellinger
CrbnBlu@aol.com