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Archive for July, 2009

System Dynamics Conference in Albuquerque

July 21st, 2009 No comments

System Dynamics Society We’re looking forward to connecting with folks at the 27th Annual International System Dynamics Conference in Albuquerque next week.   Karim Chichakly, Jeremy Merritt and I will be there to share the latest news, listen to your stories, and answer any questions you might have.

We hope to see you at as many of the following isee sponsored events as your schedule allows:

Monday, July 27th

8:00 – 6:00 PM isee systems Exhibit Booth Open
12:30 – 1:00 PM isee systems Exhibitor Demonstration
1:00 – 1:50 PM STELLA and iThink User Group Meeting

Tuesday, July 28th

8:00 – 6:00 PM isee systems Exhibit Booth Open
7:00 PM Barry Richmond Scholarship Award Presentation

Wednesday, July 29th

8:00 – 6:00 PM isee systems Exhibit Booth Open

Thursday, July 30th

8:30 – 10:00 AM Getting Started with STELLA and iThink Workshop (Part 1)
Modeling Dynamic Systems: Lessons for a First Course
Workshop by Diana Fisher
10:30 – 12:00 PM Getting Started with STELLA and iThink Workshop (Part 2)
1:00 – 2:30 PM Creating Simulations for the Web with iThink & STELLA Workshop

See you in Albuquerque!

Success to the Successful

July 15th, 2009 No comments

fifth_disciplineMy first introduction to the Systems Archetypes was years ago when I read Peter Senge’s book, The Fifth Discipline.  I remember relating these classic Systems Thinking stories to my own experience in business and thinking how useful it was to understand some of the problems we faced and why solutions didn’t always work out as intended.

What I’ve come to appreciate since then is how the characteristic themes of the Systems Archetypes transform across all sorts of different fields and situations — even our personal lives!

Take, for example, the basic story line of the “Success to the Successful” archetype:

When given the choice, we invest our resources where we expect them to deliver the best results.  By giving more resources to one option over another, we create a self-fulfilling prophesy whereby the favored option is perpetually more successful.

The story of the Success to the Successful archetype applies to all sorts of  situations leading to well-known patterns of behavior:

Exploring the Model Structure

We recently published a model of the Success to the Successful archetype to the web using isee NetSim. Exploring the model is a great way to understand the underlying structure of the Causal Loop Diagramsystem and think about ways to avoid the problems it creates.

You’ll also get an appreciation of how the decision policy for allocating resources can determine success rather than competence.

Running the Simulation

After you’ve explored the model, try running a simulation.  The base case scenario assumes no one has an advantage over the other.  As you can imagine, everyone is equally successful and it’s a win-win situation.  Try turning on the “Advantage A Switch”  to see how even a modest advantage for A can snowball into a disadvantage for B.  It’s surprising how quickly the gap can widen.

Using Modules to Create Models

In STELLA and iThink version 9.1, we added the ability to build models by linking together modules.  The Success to the Successful model is an example of how you can use modules to create a higher level map of your model.  This map can easily be presented as a causal loop diagram.

The beauty of modules is they simplify the process of transitioning from a CLD to a model that actually simulates.  If you’ve ever tried to convert a causal loop diagram into a stock and flow model, you can appreciate what I’m talking about!  By architecting your model into modules, you’ve got a built-in mechanism for developing your model in manageable chunks and communicating the high level causal relationships.

Matrix Arithmetic

July 14th, 2009 5 comments

iThink and STELLA support a variety of matrix operations. In this post, I will explain the following common operations and how to perform them:Matrix Cube

In the examples provided, I use five different arrays of varying dimensions. They are all defined using the subscript name Dim3, which is size 3.

a: 3×3
b: 3×3
c: 3×3
d: 3×1 [one-dimensional]
e: 3×1 [one-dimensional]

I also use two arrays based on Dim3, as well as the subscript name Dim2, which is size 2.

s: 2×3
t: 3×2

Read more…