Getting started, and one basic question

[ashiish]

Hello,

I have just started to use Vensim PLE for modeling market dynamics of mobile communication. In my team we have been doing this kind of work in Excel until now, and I decided to use SD to get over the limitations of Excel. I'm using the Vensim documentation. Once I have a working model, I will use it to get an approval for procurement of the commercial version.

Two questions:
1) What are the best books or other resources for developing competence modeling in Vensim? I have some understanding of SD concepts.

2) What's the easiest way to model an auxiliary variable decreasing 10% year on year?

[karankhosla]

Hi Ashish,

Principles of Systems by Jay W. Forrester, Business Dynamics by John Sterman, A Practical Approach to SD Modeling by Goeff Coyle are great places to start.

As for having a variable increase or decrease 10% year by year, it is best to treat it is a stock with an initial value and let it grow/shrink at a fractional growth rate of 10% per year.

Ex. If the Stock is "Annual Salary" then its inflow, "Annual Rate of increase of Salary" = "Annual Salary"*Fractional Growth Rate in Salary Per Year"

Units of "Annual Salary": [USD/Year]
Units of "Annual Rate of increase of Salary" [USD/Year/Year]
Units of "Fractional Growth Rate in Salary Per Year": [USD/USD/Year or 1/Year]


Value of Fractional Growth Rate in Salary Per Year = 0.1 [1/year]

I hope this helps,

Karan