Ventana software support forum

Posted: **Mon Apr 21, 1997 8:34 am**

Can anyone refer me to work on modelling the institutional interactions
in the tax system (not fiscal modelling). The interest is initially in
building sketches of the players in the tax system and the nature of
their various interactions as an aid to identifying issues for strategic
planning.

Secondly, where can I find some basic material on the particular issue of
modelling stocks and flows of information, in particular how to handle
the peculiar characteristics that
- an inflow increases stock
- an outflow (use) does not decrease stock (but may well directly result
in an inflow of refined information)
- for some, but not all purposes information depreciates or has a use
by date.
>From my point of view the most useful thing would be a general
introductory paper which gives an overview of these and related issues.

Thanks

Bill Godfrey
Bill Godfrey & Associates Pty Ltd
8 Reibey Place, Curtin, ACT 2605, Australia
Tel: (61) 6 282 2256
Fax: (61) 6 282 2447
email: bgodfrey@ozemail.com.au
BookWatch site: http://webtrax.com.au/BB/BookWatch.bbd

Posted: **Tue Apr 22, 1997 3:19 pm**

On Wed, 21 May 1997, Bill Godfrey wrote:

[...]
> Secondly, where can I find some basic material on the particular issue of
> modelling stocks and flows of information, in particular how to handle
> the peculiar characteristics that
> - an inflow increases stock
> - an outflow (use) does not decrease stock (but may well directly result
> in an inflow of refined information)
> - for some, but not all purposes information depreciates or has a use
> by date.

An outflow DOES decrease a stock. It may be offset by some inflow, but an
outflow is, as it says, flowing out, like the drain on a tub.

However, a causal influence based on information about a stock does not
decrease the stock. (Population does not decline when information about
population is used to compute population density or food per person. Beer
in a glass does not decrease when someone perceives how full it is --
someone has to drink it.) Is this what is at issue?

As for information "decpreciating" over time, Id say it is not common to
encounter such dynamics, at least as I understand the words here. One can
easily model "old" information as information that is SMOOTHed over time,
thus lagging the dynamics of the system by some specified lag time. One
can easily place lower weight on older information in some decision
process. But I guess I would be puzzled by a formulation that
"decpreciates" some information quantity eventually down to zero, since
that zero itself is information and probably not the information the
modeler intends.

Good texts in the field are the manuals that come with STELLA/iThink (HIgh
Performance Systems), Wolstenholmes System Enquiry (Wiley), and
Richardson and Pughs old book Introduction to System Dynamics Modeling
with DYNAMO (Productivity Press). The web page at MIT for the "Roadmaps"
introduction (http://sysdyn.mit.edu) is useful also but may not go into
this subtle information issue.

...GPR

-----------------------------------------------------------------------
George P. Richardson G.P.Richardson@Albany.edu
Rockefeller College of Public Affairs and Policy Phone: 518-442-3859
University at Albany - SUNY, Albany, NY 12222 Fax: 518-442-3398
-----------------------------------------------------------------------

Posted: **Thu May 22, 1997 9:32 am**

On the nature of system dynamics and modeling, perhaps the following will
be useful to you.
-----------------------------
You can get a system dynamics bibliography that has over 3000 entries:

To order the system dynamics bibliography,
specify IBM type PC, or Macintosh

Send $35 in US$ drawn on a US bank to:

System Dynamics Society
Roberta Spencer, Executive Director
Milne 300--Rockefeller College
State University at Albany
Albany, NY 12222 USA

tel: 1-518-442-3865=DD
fax: 518-442-3398
email: System.Dynamics@albany.edu

Three formats are available:

1. For Endnote, a very effective bibliography software available for either
Macintosh or PC from:

Niles & Associates, Inc
800 Jones St.
Berkeley, CA 94710 USA

Tel: 510-559-8592
Fax: 510-559-8683
Internet: nilesinc@well.sf.ca.us

I use Endnote and recommend it and use it to search for the references.

2. An exported version with field delimiters that presumably can be loaded
into some other kind of database.

3. A listing that one can look at in a word processor and do some simple
finding operations.

The bibliography can also be downloaded from:
http://www.std.com/vensim/SDBIB.HTM
-----------------------------------------------

The publications list of the System Dynamics Group at MIT is available on
the web as an Adobe Acrobat document from:
=46TP://Sysdyn.MIT.edu/Ftp/sdep/papers/D-3059-43.pdf

---------------------------------------
Membership in the System Dynamics Society and subscription to the System
Dynamics Review
are US$80 per year for regular members
and US$40 for students.
Send application to:

John Wiley & Sons
Periodicals Division, System Dynamics Review
P.O. Box 7247 8491
Philadelphia, PA 19170

or to

John Wiley & Sons
Journals Administration, System Dynamics Review
1 Oldlands Way
Bognor Regis
West Sussex PO22 9SA

-------------------------------------
There is a system dynamics discussion group on the Internet.
To join, send email to: majordomo@world.std.com
In the body of the message, enter the following two lines:

Subscribe system-dynamics
End

More system dynamics information is available at:
http://www.std.com/vensim/sdmailing.html
------------------------------------
The next annual international conference of the System Dynamics Society
will be in Istanbul, Turkey in 1997, August 19-22. Write to the System
Dyanmics Society,

System Dynamics Society
Roberta Spencer, Executive Director
Milne 300--Rockefeller College
State University at Albany
Albany, NY 12222 USA
tel: 1-518-442-3865=DD
fax: 518-442-3398
email: System.Dynamics@albany.edu
or go to the web page at:
http://ieiris.cc.boun.edu.tr/sd97
----------------------------------------

Many of the major system dynamics books are available from:

PRODUCTIVITY PRESS
541 N.E. 20th Avenue
Portland, OR 97232, USA

tel: 503-235-0600
fax: 503-235-0909

Web page: http://www.ppress.com/
email: staff@ppress.com

Alfeld, Louis Edward, and Alan K. Graham. 1976. Introduction to Urban
Dynamics. Portland, OR: Productivity Press. 333 pp.

=46orrester, Jay W. 1961. Industrial Dynamics. Portland, OR: Productivity
Press. 464 pp.

=46orrester, Jay W. 1968. Principles of Systems. (2nd ed.). Portland, OR:
Productivity Press. 391 pp.

=46orrester, Jay W. 1969. Urban Dynamics. Portland, OR: Productivity Press.
285 pp.

=46orrester, Jay W. 1971. World Dynamics. (1973 second ed.). Portland, OR:
Productivity Press. 144 pp. Second edition has an added chapter on
physical vs. social limits.

=46orrester, Jay W. 1975. Collected Papers of Jay W. Forrester. Portland, OR=
:
Productivity Press. 284 pp

Posted: **Sat May 24, 1997 6:41 am**

Regarding Georges response on depreciation:
I could imagine modeling a drain from a stock of useful information which
would represent information becoming obsolete. Youd probably model it as
exponential decay.
Maybe there are some financial/accounting circumstances in which you
might depreciate the $ value of information, of say an acquired company.
I put a little structure on our web site that will do that.
www.hps-inc.com. Click on the Support Button, then click on Modeling
Tricks.

***************************************************************************

Phil Odence
High Performance Systems
45 Lyme Road, Suite 200
Hanover, NH 03755
voice- 603 643 9636 x107, fx- 603 643 9502, web- http://www.hps-inc.com

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Modelling of tax system

Modelling of tax system

Modelling of tax system

Modelling of tax system

Modelling of tax system