Date: Thursday, 17th of September 2009 17:08:07 -0500 (CDT) From: Mark Jacobson To: 810-025-01-fall@uni.edu Subject: Turn in Vensim assignment by noon Tuesday is okay... Hi 025 students, http://www.cs.uni.edu/~jacobson/025/ Since there seemed to be some confusion on the assignment and since I goofed and forgot to put up the web page mentioned on your assignment handout, we will extend the due date for the assignment to: Noon on Tuesday of next week, which is: September 22nd at noon ---------------------- Tuesday You will send me two attachments: Mail to jacobson@cs.uni.edu -- or jacobson@cns.uni.edu --- CS for Computer Science or CNS for College of Natural Science 1. Attach the Vensim file you created to the email note that you send to jacobson@cs.uni.edu so I can look at your model and run it and grade it. 2. Attach the Microsoft Word or whatever file you created that has the GRAPH of your simulation and the TABLE of your simulation. (ALTERNATIVELY, it is OKAY for you to turn in a printout of these two things, if you have trouble getting them pasted into Microsoft Word. There is an icon just to print them when you are looking at a GRAPH or a TABLE in Vensim. As discussed in class today, the following Chapter 02 file from the Modeling the Environment book has all the details you need for the assignment, along with your photocopied handouts, which have excerpts of the most useful parts of Chapter 02 for doing your homework. Here are some excerpts, that help you see some of the values for the CONVERTORS that are needed. Chapter 02: Software: (preview draft) Getting Started with Stella and Vensim PDF file. http://www.wsu.edu/~forda/Ch%202.pdf http://www.wsu.edu/~forda/AA2nd.html has an easier link to Chapter 2: Software and shows what the textbook will look like when it gets published in November. Page 04 of Chapter 02 --------------------- Set the initial value of the population to 100 and the births to be the product of the population and the birth rate. Set the birth rate to 0.07, and Vensim will respond with a diagram free of highlighted variables. The model is ready to simulate. Go to the model command and drag down to settings, and ask for time bounds. Set time to be in years with an initial time of 0 and a final value of 40. Page 04 of Chapter 02 --------------------- Population Growth with Births and Deaths The first model simulated the cumulative effect of births, but it ignored deaths. Suppose we are told that the death rate is 2% per year. If the population has been growing at 7%/yr, we would suspect the birth rate is 9% per year. Fig. 2.11 shows a new version of the model with deaths, a flow which drains the stock of population. Page 05 of Chapter 02 --------------------- The main changes are the extra converters to help us explain the births. Lets assume that the fraction female is 0.5 and 36% of the females are biologically mature. And finally, lets assume that the mature females give birth every other year. This means that the births per mature female per year is 0.5. Pages 05 and 06 of Chapter 02 ----------------------------- If you work through the numbers, you'll see that this combination of assumptions corresponds to a birth rate of 9%/year, the same value as in the previous model. The new model gives the correct results, and it provides a fuller explanation of the reasons for the exponential growth in population http://www.cs.uni.edu/~jacobson/025/ Thanks, Mark jacobson@cs.uni.edu