QUERY Discrete event software (002)

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Bill Braun <bbraun@hlthsys.co
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QUERY Discrete event software (002)

Post by Bill Braun <bbraun@hlthsys.co »

Posted by Bill Braun <bbraun@hlthsys.com>

I am involved in a project where I may need to contrast SD and discrete
event simulation. I want to avoid significant investment until the
future path becomes clear.

I would appreciate suggestions/recommendations on open source and/or low
cost packages. The software should be GUI based (like Vensim, Powersim,
iThink, etc.).

Thank you,

Bill Braun
Posted by Bill Braun <bbraun@hlthsys.com>
posting date Mon, 31 Dec 2007 18:22:39 -0500
_______________________________________________
Bill Harris <bill_harris@faci
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Posts: 51
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QUERY Discrete event software (002)

Post by Bill Harris <bill_harris@faci »

Posted by Bill Harris <bill_harris@facilitatedsystems.com>

""SDMAIL Bill Braun"" <bbraun@hlthsys.com> writes:
> I am involved in a project where I may need to contrast SD and discrete
> event simulation. I want to avoid significant investment until the
> future path becomes clear.

Bill B.,

I think there's a thread about this from a few years back. I recall it,
because I recall making the point that SD and discrete event form a
false dichotomy: SD is all about feedback and accumulation, which can be
done in continuous or discrete time and with quantized or non-quantized
levels. (I really remember that because John Sterman followed up with
""Bill Harris is right!"", which I /so/ wanted to post on my Web site :-) .)

> > I would appreciate suggestions/recommendations on open source and/or low
> > cost packages. The software should be GUI based (like Vensim, Powersim,
> > iThink, etc.).

I presume what you want is what normally is called discrete event
simulation: no inherent feedback (it may be harder to find a tool that
allows no feedback) and quantized time and perhaps levels, right?

CPNTools (http://wiki.daimi.au.dk/cpntools/cpntools.wiki) is a (the?)
GUIfied tool for Colored Petri Nets. I'm not sure what the status of
its graphical output capabilities is; I haven't really used it in a
while. You'll have to decide if a CPN fits your needs, and you do need
to program bits of a model (guards, arc expressions, declarations, etc.)
in a subset of ML.

SimPy (http://simpy.sourceforge.net/) seems to be a (the?) major
contender in that world today. It's on my list to learn; I've just
played around with it a bit so far. It has a GUI but perhaps not in the
sense you mean: you can program a GUI to provide a user interface for
others, but you still program the model in Python.

I sense that either would be robust enough to do production work, as
long as they have the capabilities you seek. Both are no-cost solutions.

Having said all that, perhaps I should have started by asking what you
really need to do. That might focus the answers better; mine were just
quick, off-the-cuff responses.

I hope that helps; I'll be curious what others say.

Bill
- --
Bill Harris
Posted by Bill Harris <bill_harris@facilitatedsystems.com>
posting date Fri, 04 Jan 2008 20:21:38 -0800
_______________________________________________
<wakeland@pdx.edu>
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Posts: 2
Joined: Fri Mar 29, 2002 3:39 am

QUERY Discrete event software (002)

Post by <wakeland@pdx.edu> »

Posted by <wakeland@pdx.edu>

Bill Braun says: ""I would appreciate suggestions/recommendations on
open source and/or low cost [DES] packages""

I don't know about open source options, but Extend from Imaginethat,
Inc. would be a good commercial package to look at. Demo and
educational versions are available:

http://www.extendsim.com/

Another good DES package, which has more powerful statistical analysis
tools, is Arena from Rockwell:

http://www.arenasimulation.com/

Wayne Wakeland
Systems Science Graduate Program
Portland State University
Posted by wakeland@pdx.edu
posting date Fri, 04 Jan 2008 22:25:42 -0800
_______________________________________________
""Jim Thompson"" <james.thomp
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Posts: 21
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QUERY Discrete event software (002)

Post by ""Jim Thompson"" <james.thomp »

Posted by ""Jim Thompson"" <james.thompson@strath.ac.uk>

Bill,

Have a look at the Strathclyde management science Web site and
http://www.dmem.strath.ac.uk/~pball/sim ... ulate.html. It's not
precisely what you asked but it may kick start your search. Strathclyde has
extensive discrete event experience, and the management science faculty
could help direct your search.

Michael Pidd's books, 'Computer Simulation in Management Science' and 'Tools
for Thinking: Modelling in Management Science', are handy reference works.

SD simulation techniques are aimed at the sort of problems to be solved:
system design and management policy. Discrete event simulation is aimed to
understand the detail complexity of a system's dynamics. So if the problem
is policy design (say, allocation of resources) traditional SD simulation is
efficient. If the problem is policy implementation (say, the budgeting
process) discrete event simulation is efficient.

I expect you will get several responses with a philosophical bent and
apologize in advance for this one.

Jim Thompson
Posted by ""Jim Thompson"" <james.thompson@strath.ac.uk>
posting date Sat, 5 Jan 2008 10:09:50 -0500
_______________________________________________
Bill Harris <bill_harris@faci
Senior Member
Posts: 51
Joined: Fri Mar 29, 2002 3:39 am

QUERY Discrete event software (002)

Post by Bill Harris <bill_harris@faci »

Posted by Bill Harris <bill_harris@facilitatedsystems.com>

""SDMAIL Bill Braun"" <bbraun@hlthsys.com> writes:
> I am involved in a project where I may need to contrast SD and discrete
> event simulation. I want to avoid significant investment until the
> future path becomes clear.

Bill B.,

I think there's a thread about this from a few years back. I recall it,
because I recall making the point that SD and discrete event form a
false dichotomy: SD is all about feedback and accumulation, which can be
done in continuous or discrete time and with quantized or non-quantized
levels. (I really remember that because John Sterman followed up with
""Bill Harris is right!"", which I /so/ wanted to post on my Web site :-) .)

> > I would appreciate suggestions/recommendations on open source and/or low
> > cost packages. The software should be GUI based (like Vensim, Powersim,
> > iThink, etc.).

I presume what you want is what normally is called discrete event
simulation: no inherent feedback (it may be harder to find a tool that
allows no feedback) and quantized time and perhaps levels, right?

CPNTools (http://wiki.daimi.au.dk/cpntools/cpntools.wiki) is a (the?)
GUIfied tool for Colored Petri Nets. I'm not sure what the status of
its graphical output capabilities is; I haven't really used it in a
while. You'll have to decide if a CPN fits your needs, and you do need
to program bits of a model (guards, arc expressions, declarations, etc.)
in a subset of ML.

SimPy (http://simpy.sourceforge.net/) seems to be a (the?) major
contender in that world today. It's on my list to learn; I've just
played around with it a bit so far. It has a GUI but perhaps not in the
sense you mean: you can program a GUI to provide a user interface for
others, but you still program the model in Python.

I sense that either would be robust enough to do production work, as
long as they have the capabilities you seek. Both are no-cost solutions.

Having said all that, perhaps I should have started by asking what you
really need to do. That might focus the answers better; mine were just
quick, off-the-cuff responses.

I hope that helps; I'll be curious what others say.

Bill
- --
Bill Harris
Posted by Bill Harris <bill_harris@facilitatedsystems.com>
posting date Fri, 04 Jan 2008 20:21:38 -0800
_______________________________________________
""Magdy Helal"" <mhelal@mail.
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QUERY Discrete event software (002)

Post by ""Magdy Helal"" <mhelal@mail. »

Posted by ""Magdy Helal"" <mhelal@mail.ucf.edu>

Hi Bill,

I'm working on an approach to integrate SD and discrete event
simulation. There is this paper that we published in the SD
conference in July 07 at this link:

http://www.systemdynamics.org/conferenc ... LAL482.pdf

The title is very explicit: A methodology for Integrating and
Synchronizing the System Dynamics and Discrete Event Simulation
Paradigms

I think it can be of interest to you and I will appreciate your
comments and feedback about the approach described in it.

Regards

Magdy Helal
Office of University Analysis & Planning Support
University of Central Florida
12424 Research Parkway, Suite 215
Orlando, Florida 32826
Posted by ""Magdy Helal"" <mhelal@mail.ucf.edu>
posting date Sat, 05 Jan 2008 22:38:59 -0500
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Bill Harris <bill_harris@faci
Senior Member
Posts: 51
Joined: Fri Mar 29, 2002 3:39 am

QUERY Discrete event software (002)

Post by Bill Harris <bill_harris@faci »

Posted by Bill Harris <bill_harris@facilitatedsystems.com>

""SDMAIL Jim Thompson"" <james.thompson@strath.ac.uk> writes:

> So if the problem
> is policy design (say, allocation of resources) traditional SD simulation is
> efficient. If the problem is policy implementation (say, the budgeting
> process) discrete event simulation is efficient.

Jim,

Good, easy to remember distinction. Just a caution for people new to
this (I'm sure you know it): problems in policy implementation /may/ be
due to problems in policy design.

Bill
- --
Bill Harris
Posted by Bill Harris <bill_harris@facilitatedsystems.com>
posting date Sun, 06 Jan 2008 09:37:27 -0800
_______________________________________________
George Richardson <gpr@albany
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Posts: 20
Joined: Fri Mar 29, 2002 3:39 am

QUERY Discrete event software (002)

Post by George Richardson <gpr@albany »

Posted by George Richardson <gpr@albany.edu>

Beyond the questions of software and integration of approaches are
questions about the nature of ""reality"" that have puzzled me about
discrete event simulation. (Of course, others have questioned the
fit between reality and our continuous time, feedback-based point of
view, but I think I've come to terms with those issues.)

A discrete event approach seems to need to assume that nothing happens
between events. (Is that a correct characterization of the approach?)
An event occurs, people and their systems adjust to the new event
immediately (whatever ""immediately"" means in a given application) and
then nothing changes until the next event.

I'm uncomfortable with that, as I think the ""real world"" is full of
accumulating pressures leading up to events and following on after them.
Things happen in between events -- people gradually change their
perceptions, pressures build for other responses even after immediate
responses to an event, and the pressures that built to cause or influence
an event continue to change after the event and before the next one.

Am I capturing this correctly? How does a devotee of discrete event
simulation think about these issues?

..George

George P. Richardson
Chair of public administration and policy
Rockefeller College of Public Affairs and Policy
University at Albany - SUNY, Albany, NY 12222
Posted by George Richardson <gpr@albany.edu>
posting date Mon, 7 Jan 2008 09:47:47 -0500
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""Louis Macovsky"" <dynbiosys
Junior Member
Posts: 5
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QUERY Discrete event software (002)

Post by ""Louis Macovsky"" <dynbiosys »

Posted by ""Louis Macovsky"" <dynbiosys@verizon.net>

Magdy Helal wrote:
>The title is very explicit: A methodology for Integrating and
>Synchronizing the System Dynamics and Discrete Event Simulation
>Paradigms

Magdy,

Have you looked at using your approach to add SD to Ptolemy (UCBerkeley
http://ptolemy.eecs.berkeley.edu/ ). From your paper it ""appears"" that it
may be a fit (I am not qualified to say it is or not). If it could be
programmed to be a module in Ptolemy, I believe it could open doors to a
number of experiments in hybrid modeling. If it was
integrated into Ptolemy, I would look for an ecological or environmental risk assessment
project using Kepler http://kepler-project.org/Wiki.jsp?page=KeplerProject .

Lou

Posted by ""Louis Macovsky"" <dynbiosys@verizon.net>
posting date Mon, 07 Jan 2008 18:00:28 -0800
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""Ulrey, Michael L"" <michael
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QUERY Discrete event software (002)

Post by ""Ulrey, Michael L"" <michael »

Posted by ""Ulrey, Michael L"" <michael.l.ulrey@boeing.com>

Bill,

I am very interested in this issue, as the kinds of problems I
work on can benefit from many different modeling paradigms, including
SD, discrete event simulation (DE), and agent-based modeling (AB). There
is a very good paper which contrasts and compares the different
approaches:
http://www.systemdynamics.org/conferenc ... 1BORSH.pdf .
The tool described in this paper is called AnyLogic, and allows a
mix-and-match of the SD, DE, and AB paradigms.

Another tool that claims to combine SD and DE modeling paradigms
is GoldSim: http://www.goldsim.com/Content.asp?PageID=197 contains a
contrast-and-compare discussion between the two.

Years ago I developed a reliability tool for aerospace
applications within a DE tool called BONeS (Block Oriented Network
Simulator). I feel that BONeS was the best such tool I ever used.
Unfortunately, it is no longer supported in its original form, although
it has risen Phoenix-like from the ashes in a tool called MLDesigner:
http://www.mldesigner.com/mldesigner.html . Another Windows-based DE
tool is called MicroSaint: http://www.maad.com/index.pl/micro_saint

There is one other suggestion I have, which is TOPAZ from NLR,
the Dutch Aerosapce Laboratories. This is very specifically oriented
towards air traffic management applications, but it is very advanced in
its combining of so-called Dynamically-Colored Petri Nets (DCPN),
pioneered by NLR (Henk Blom and Mariken Everdij and Bert Bakker), which
combines the continuous dynamics of airplane trajectories with the
discrete actions of pilots, controllers, automation, etc. Here is but
one example of the many applications of this approach:
http://www.nlr.nl/id~4262/lang~en.pdf

Cheers, Mike

Dr. Michael L. Ulrey
Air Traffic Management
The Boeing Co.
Posted by ""Ulrey, Michael L"" <michael.l.ulrey@boeing.com>
posting date Mon, 7 Jan 2008 08:55:33 -0800
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Fabian Fabian <f_fabian@yahoo
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QUERY Discrete event software (002)

Post by Fabian Fabian <f_fabian@yahoo »

Posted by Fabian Fabian <f_fabian@yahoo.com>

Hi All,

Just adding to Bill's reflection, in real life, problems may have two
levels of aggregation working concurrent and interdependently, one of
them more suitable for being modeled with SD software, and the other
by DES or ABS.

Examples abound, e.g. how supply network dynamics affect brand
attractiveness (DES/SD); autonomous agents buying/selling stocks and
the related impact on the stock market (ABS/SD).

Mag Helal paper is very good in explaining integration and
sinchronization of DES and SD models.

Here at ITBA, Arena is used for DES in the related courses (Simulation;
and Operations Research).

In SD, we have built a draft of a mix of a conceptual, and of a specified
model integrating Systems thinking with an ABS simulation model, humbly
built with MS Excel, though there are more suitable tools for ABS such
as starlogo and other SWARM tools.

Sometimes the problem has more complex characteristics, suitable for
modeling with SD&DES&ABS. The tool for that purpose would be Anylogic ,
from XJTek.

Sorry that I couldn't offer info about freeware.

Cheers,

Fabian Szulanski
Director
System Dynamics Centre
Instituto Tecnologico de Buenos Aires
Posted by Fabian Fabian <f_fabian@yahoo.com>
posting date Mon, 7 Jan 2008 07:28:16 -0800 (PST)
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Khalid Saeed <saeed@wpi.edu&g
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QUERY Discrete event software (002)

Post by Khalid Saeed <saeed@wpi.edu&g »

Posted by Khalid Saeed <saeed@wpi.edu>

George,

A beautiful explanation! I wish to add that policy or decision rules
in system dynamics are based not on discrete decisions, but on patterns
of decisions. These patterns may vary according to the time frame over
which a decision pattern is observed.

There are also mechanical problems with subsuming a discrete structure
in a continuous model that might result in dynamics created by the
stiffness of the model rather than the behavior of the system it
represents.

I view combining discrete and continuous structures in system dynamics
models with reservation even though software might allow this.

Best,

Khalid
Khalid Saeed, PhD
Professor of Economics and System Dynamics
Social Science and Policy Studies Department
WPI, Worcester, MA 01609
Posted by Khalid Saeed <saeed@wpi.edu>
posting date Tue, 8 Jan 2008 13:13:13 -0500
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Bill Harris <bill_harris@faci
Senior Member
Posts: 51
Joined: Fri Mar 29, 2002 3:39 am

QUERY Discrete event software (002)

Post by Bill Harris <bill_harris@faci »

Posted by Bill Harris <bill_harris@facilitatedsystems.com>

""SDMAIL George Richardson"" <gpr@albany.edu> writes:
> Beyond the questions of software and integration of approaches are
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

George,

With all the suggestions of commercial software that does both DE and SD
simulation, I wanted to mention one of the early GPL'd packages that
does all of this and more: Paul Fishwick's SimPack. It is a C language
system that supported his notion of multi-modeling, in which one might
have models, sub-models, and sub-sub-models (and so forth) where each
model might be built using a different methodology. So you could have,
for example, a top-level finite state automaton that, depending upon the
time of day and day of the week, could invoke one of several SD models
that would describe the behavior of shoppers in a grocery store. One
might inquire about the purpose of such a model and why it might be more
attractive than other alternatives, but that's the sort of thing it can
do.

In the FAQ of the once active comp.simulation USENET group, SimPack was
listed as one of the basic tools for a simulationist's toolkit. Paul
wrote a book about SimPack called Simulation Process Design and
Execution. I wrote an article for The Systems Thinker (System Dynamics
on a Shoestring) that told how to do SD simulation using SimPack
(http://www.thesystemsthinker.com/nldata ... ItemID=590).

> > A discrete event approach seems to need to assume that nothing happens
> > between events. (Is that a correct characterization of the approach?)

I'd not classify myself as a devotee of DE simulation, but I have used
it. I'd perhaps modify your sentence to, ""A discrete event approach
seems to need to assume that nothing _of current interest_ happens
between events."" (Horses for courses and all that).

Does that help? I suspect it may be a fairer portrayal, but you might
still question whether something in the time between events /should/ be
of current interest.

Not having used DE simulation in a while, I'm curious: when people here
speak of the need for the DE methodology, to what are they referring?
What do they understand as DE simulatino?

Is it the ability to track characteristics of individual entities
without using coflows (i.e., discrete entities in the conserved
flows)?

Or is it more the focus on discrete time: the ability, for example, to
model queueing behavior stochastically?

Or do DE models communicate better to certain groups less familiar
with SD and uncomfortable with the level of aggregation we tend to
use?

Bill
- --
Bill Harris
Posted by Bill Harris <bill_harris@facilitatedsystems.com>
posting date Tue, 08 Jan 2008 09:22:29 -0800
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""John Morecroft"" <jmorecrof
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QUERY Discrete event software (002)

Post by ""John Morecroft"" <jmorecrof »

Posted by ""John Morecroft"" <jmorecroft@london.edu>

Bill,

There are a few corrections I'd like to mention for your summary of SD
and DES. In the section on PAPERS/ARTICLES/BOOKS there is the following
reference: ""Explaining Puzzling Dynamics: Comparing the Use of System
Dynamics and Discrete-Event Simulation"" By John Morecroft

http://www.systemdynamics.org/conferenc ... REC107.pdf

In fact I co-authored the article with Stewart Robinson who is an expert
in discrete-event simulation at Warwick Business School. The link takes
you to a pdf of the paper we presented at the International Conference of
the System Dynamics Society, Boston, July 2005. The paper can also be
found on the System Dynamics Society website. Incidentally, we are currently
submitting a revised version of the paper for journal publication and I'll let
you know the citation details when we have cleared the review hurdles.

Later in your summary there is a section on MODELS that lists 'Companion ithink
models to Morecroft's paper':

NONE OF THESE MODELS ARE MINE except the last one which is based on a
deliberately small and transparent fisheries model I developed for the
Boston 2005 paper. In the Boston paper it is compared with an equally
small and transparent discrete-event fisheries model developed
independently by Stewart Robinson. You can find fully documented versions
of my original SD fisheries models in Chapters 1 and 9 of my new book
'Strategic Modelling and Business Dynamics'. In the appendix of Chapter 9
you will also find some reflections about SD and DES.

http://www.wileyeurope.com/college/morecroft

Regards John

_______________________________

Dr. John Morecroft | Senior Fellow | Management Science and Operations
London Business School | Regent's Park | London NW1 4SA | United Kingdom
Posted by ""John Morecroft"" <jmorecroft@london.edu>
posting date Thu, 10 Jan 2008 18:23:20 -0000
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