Current software in system dynamics

[Kedwards Tim TJ]

Dear All,

I am currently considering which software package would best suit my needs.
I have looked at the demo versions of PowerSim, STELLA/iThink and Vensim for
PC and am left somewhat in a state of confusion !

The first I looked at was PowerSim, very quick, easy(ish) to use and seems
quite powerful. Then came iThink and somewhat of a disappointment with it
being considerably slower and more confusing to use. Vensim - well - seems
about the same !

Are there any others I should consider ? I used to use ISIM many years ago -
and all these seem to be unsurprisingly way ahead of it. I am still awaiting
to see what Dynamo is !

The package will mainly be used to model & investigate interacting
biological populations under different variable setups - ranging from single
species dynamics to predator-prey etc etc

Any advise would be gratefully received

Best wishes

Tim


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dr Tim Kedwards
ZENECA Agrochemicals
Ecological Risk Assessment Section
Jealotts Hill Research Station
Bracknell, UK
RG42 6ET

Tel: +44 (0) 1344 414107
Fax: +44 (0) 1344 414124
Email: Tim.T.J.Kedwards@gbjha.zeneca.com
Disclaimer:- The opinions expressed herein are my personal opinions
and do not necessarily represent those of my employer

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

[Jay Forrest]

Hi Tim!

Your comments should raise a lively response!

>I am currently considering which software package would best suit my needs.
>I have looked at the demo versions of PowerSim, STELLA/iThink and Vensim for
>PC and am left somewhat in a state of confusion !

I own all three, Stella, Vensim, and Powersim. In my opinion, each has its
strengths and weaknesses. Based upon my observation of the programs over
several years I must comment that the "leadership role" seems to rotate
among the three as one brings out a new version, another ups the ante, etc.

I am intrigued that you find Stella and Vensim more confusing than Powersim.
I would describe Stella as a more "formal" system modeling program - closer
to the system dynamic concepts presented by Jay Forrester. I find Stella
very straightforward in concept though I do find its interface less
appealing. The biggest challenge to a beginner in Stella IMO is that you
must follow the symbolic formality of pure SD - for example you cannot link
a constant to a level.

I started with Vensim and find it faster because of its interface. (If
nothing else the tool does not have to be reselected at each step!) (Yeah, I
know about the Alt key in Stella, but Vensim stays with the same tool until
you change it and I like that better!) I also suspect that my modeling
background and philosophy more closely match that behind Vensim than Dr.
Forresters pure system dynamics. (Vensim is a causal loop modeling tool
which emulates SD. The result is that the focus is on the diagram and
links. You can connect anything to anything (constant to level, level to
level, etc.) As an experienced modeler who started outside of SD I find
this freedom very helpful. I also find it more useful as a "flow/logic"
diagram tool. I do most of my work in Vensim.

I am relatively new to Powersim. The interface is good - it is graphically
slightly prettier than Vensim, though, like Stella, it changes the tool
after each step. I see Powersim as similar to Stella in enforcing SD
formality. I also feel it has a longer learning curve.

My status. I generally use Vensim for my personal work. I use Powersim when
the desired outcome is a flight simulator. I would use Stella when it is
preferred or required by a client.

Hope this helps!
Jay Forrest
pteragen@neosoft.com

Pteragenesis
Chaos, Complexity, System Dynamics, Studies of the Future
pteragen@neosoft.com
http://www.neosoft.com/~pteragen
(713)493-5022 (voice) (713)493-6715 (fax)

[carolus]

L.S.,
A couple of weeks ago Tim Edwards asked the following

>I am currently considering which software package would best suit my needs.
>I have looked at the demo versions of PowerSim, STELLA/iThink and Vensim for
>PC and am left somewhat in a state of confusion !

Subsequently, some people responded and commented on the pros en cons
of the packages.

However, most respondents didnt mention the version they have been working
with or on what type of machine they have tried it.
I think it matters whether one compares the latest Vensim on a windows/95
machine running 150 Mhz with one of the earliest versions of Stella ...on
say a Macintosh Classic, and vice versa.

In others words, I still dont know whether package A should be preferred
to B and on what machine.

I would like to suggest that those who were so kind to inform us,
should do this again but then in, lets say a standard format such as:

mentioning:
1.: the platform, Operating System, processor, memory
and
2.: the software package version-number
elease
and.:
3.: size of the model used ?

Thanks,


+++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Carolus Grutters

Recht en Informatica Law and IT
Faculteit der Rechtsgeleerdheid Faculty of Law
KU Nijmegen, University of Nijmegen

phone: +31 -24 -361.57.01 P.O. Box: 9049
fax: +31 -24 -361.61.45 6500 KK Nijmegen
email: carolus@jur.kun.nl The Netherlands
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++

[ladd@ldgo.columbia.edu (John Lad]

Please direct me to the source for PowerSim and Vensim. How do I get ahold
of emos for these two??

Thanks

John Ladd
ladd@ldgo.columbia.edu
914-923-1108
-----------------------------------
The following is from the welcome message to this mailing list:

Vensim (Software)

Ventana Systems, Inc. publishes and sells the Vensim software.
For information contact:

Ventana Systems, Inc.
149 Waverley Street
Belmont MA 02178
Phone 617 489 5249
Fax: 617 489 5316
e-mail vensim@world.std.com
http://www.std.com/vensim

iThink (Software)

High Performance Systems publishes and sells the iThink software.
For information contact:

High Performance Systems
45 Lyme Road Suite 300
Hanover NH 03755
Phone: 603 643 9636
Fax: 603 643 9502
Email:support@hps-inc.com
WWW:http://www.hps-inc.com/

PowerSim (Software)

ModelData AS publishes and sells the PowerSim software.
For information contact:

POWERSIM AS POWERSIM CORPORATION
PO Box 206, Knarvik Senter 1175 Herndon Parkway Suite 600
5100 ISDALSTOE Herndon VA 20170
NORWAY USA
Phone: 47 5634 2400 Phone: 703 481 1270
Fax: 47 5634 2401 Fax: 703 481 1271
Email: powersim@modeld.no Email: powersim@powersim.com
WWW: http://www.psiminst.com/

Dynamo (Software)

Pugh-Roberts publishes and sells the Dynamo software. For information

Pugh-Roberts Associates
41 William Linskey Way
Cambridge MA 02142
Phone: 617 864 8880
Fax: 617 864 8884

--------------------------------

[jwang@echo-on.net (James J. Wang]

>I am currently considering which software package would best suit my needs.
>I have looked at the demo versions of PowerSim, STELLA/iThink and Vensim for
>PC and am left somewhat in a state of confusion !

As far as I know, all software you mentioned are good. ithink/Stella
is good because it is very straightforward. If your need is to understand
yous systems, the package provides you various architypes and wonderful
documents, which really make your work easier. The disadvantage is ithink/
Stella was originally coded for MAC machine. The tansformation from MAC to
IBM clones reduces the software performance significantly.

PowerSim is very similar with ithink/Stella, however its native code for
Intel machine gives the software some genetic advantages. I have not seen
the most recent release of PowerSim. My impression is PowerSim is good
for those professional SD literated people. The lack of methedology
documents makes software less friendly to those people with limited SD
knowledge.

Vensim has an outstanding feature of model calibration. For those
whose main concerns is building customized model with their data sources.
Vensim may be a beter choice.

If your first objective is tracking your system response/performance,
rather than understanding the system itself you may go to some other
sophisticated simulation package, like SIMULINK
(http://www.mathworks.com/simulink.html) or dynasim
http://www.Dynasim.se/ and many others may be your choice.

I would say the methedology selection should based on your needs.
I have been working with System Dynamics for many years, I may say
the software developed for System Dynamics is not precise enough
to be used for computer simulation of real system, however, all of them
are just good enough for conceptual simulation which may enhance your
learning capability dramatically.

JIE

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_/_/_/_/_/ _/ _/ _/ __/_/_/ _/ _/ _/_/_/_/ Wang Jie
_/ _/ _/ _/ _/ _/ _/_/ _/ _/ 283 Wolverleigh Blvd.
_/ _/ _/_/ _/ _/_/_/_/ _/ _/ _/ _/ _/_/Toronto Ont. M4C 1S3 Canada
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_/_/ _/_/ _/ _/ _/ _/ _/ _/ _/_/_/ Tel: (416)-696-2324
Email: jwang@echo-on.net
===============================================================================

[forda@mail.wsu.edu (Andy Ford)]

This is Andy Ford at WSU replying to Tim Kedwards inquiry about the software
to use in biological population modeling such as predator prey models:
I use Stella in an undergraduate Environmental Science course on
building System Dynamics models. It works quite well. The students use
Stella in the laboratory or they may buy their own at the bookstore. They
see a predatory prey model mid way through the course, and the "animation"
feature of Stella comes in quite handy when portraying the cyclical nature
of the population interactions. ,


----------------------------------------------------------
Andy Ford
Program in Environmental Science and Regional Planning
Washington State University
Pullman, WA 99164-4430
(509) 335-7846
FordA@mail.wsu.edu
----------------------------------------------------------

[Stephen Wehrenberg]

Vensim has a nice demo and free "Personal Learning Edition" at their
home page, http://www.std.com/vensim/VENSIM.HTM.

Powersim Institute home page is http://www.psiminst.com/ ... dont
recall if their demo cersion is on line or if you ahve to ask for it.
Its quite a package, 4-5 floppies.

Steve


--
Stephen B. Wehrenberg, Ph.D.
Chief, Forecasts and Systems, US Coast Guard;
Administrative Sciences, The George Washington University
wstephen@erols.com
"Life is a jam session."

[Cedric Knight]

Hello, I have used both the pc and mac versions of ithink for several
years. The functionality in the pc version is as good as that in the
Macintosh. It supports Dynamic Data Entry and works very well with
spreadsheets.

cedric knight
cedric@ridgecrest.ca.us

[David Bridgeland]

At 08:53 PM 10/24/96 -0400, James J. Wang wrote:
> My impression is PowerSim is good
>for those professional SD literated people. The lack of methedology
>documents makes software less friendly to those people with limited SD

With Powersim 2.5 (the most recent release) we include two books for
those who are not yet professional SD people: "An Introduction to
System Dynamics Modeling" and "Quick Tours", a volume showing how to
model a large number of example situations.


Dave.

Dave.
David Bridgeland
davbr@powersim.com
Powersim Corporation
Herndon, Virginia
www.powersim.com

[Catriona Galbraith]

Another package you might want to look at is ModelMaker. It is a Windows
program which is a relative newcomer to the market, having been originally
developed for an environmental sciences application. The current shipping
version (2) has a demo version available for download from the web site
listed below. We are also beta-testing a new version (3) which will be of
much more interest to this group. ModelMaker is said to be one of the
easiest packages on the market to use and has a substantial collection of
model analysis tools such as optimization, minimization, sensitivity
analysis and goodness-of-fit statistics.

If you or anyone on this list in interested in taking part in the beta
testing for ModelMaker version 3, please contact catriona@cherwell.com

ModelMaker is published by
Cherwell Scientific Publishing
The Magdalen Centre
Oxford Science Park
Oxford OX4 4GA
United Kingdom

Tel: +44 (0)1865 784800
Fax: +44 (0)1865 784801
e-mail: info@cherwell.com
web site: www.cherwell.com/cherwell

In the USA contact:
Tel: (415) 852 0720
Fax: (415) 852 0723
e-mail: csp.usa@cherwell.com
--- ---
Catriona Galbraith | e-mail: catriona@cherwell.com
Development Manager | Phone: +44 (0)1865 784803
Cherwell Scientific Publishing | Fax: +44 (0)1865 784801
Oxford OX4 4GA, UK | http://www.cherwell.com/cherwell
--- ---