IST 618 Assignment 3 Nov 2023
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Nov 24, 2024
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Assignment 3
1
Mapping the Stock and Flow Structure of Systems
Assigned: Tuesday November 25, 2023; Due: Tuesday December 2,
2023
This assignment provides you with the opportunity to practice with the structure and
dynamics of stocks and flows. Stocks and flows are the building blocks from which every
dynamic system is constructed. The ability to identify, map, and understand the dynamics of
the networks of stocks and flows in a system is essential to understanding the processes of
interest in any modeling effort.
Be sure you have carefully read Ch. 6, Ch 7 and 10 of
Business Dynamics
before doing this assignment.
Submitting your work:
One member of your team should submit your team’s
write up and model on Blackboard, as a single zip (or 7Z) file containing a word
document and a Vensim mdl file. Make sure the write up lists the full names of all
members of your group.
Response of Delays to Changing Delay Times:
To develop your understanding of how the different types of delays respond to variations in the
delay time, answer the following questions.
1.
Consider a model of the post office as a third-order material delay. Assume that the mailing rate
is constant, and that the system is in equilibrium—the mailing rate and delivery rate are equal.
Without using simulation, sketch the behavior you expect if the delay time suddenly and
permanently increases from
5
days to 10 days on day
5.
Make two graphs—one showing the
mailing rate and delivery rate and the other showing what you expect to happen to the stock of
letters in transit. Sketch the response you would expect if the delay time suddenly dropped from
5
to 2.5 days.
2.
Now consider a firm’s forecast of orders. Assume the firm uses adaptive expectations to forecast
orders. Assume that the order rate is constant and that the expected order rate is equal to the order
rate (the system is in equilibrium). Without using simulation, sketch the behavior you expect if
the time to adjust the forecast suddenly and permanently decreases from 6 months to
3
months.
3.
After you’ve sketched your intuitive estimates, build the models and simulate their response to
changes in the delay time. Was your intuition correct? If there are differences in the response of
the material and information delays to changes in the delay times, explain why.
1 This assignment is modified from an assignment prepared by MIT System Dynamics Group faculty. MIT has not
endorsed any changes or modifications to the original assignment. Terms of Use, visit: http://ocw.mit.edu/terms.
4.
Create a model of the improvement process described above and compare its behavior to
the given data. Once you have formulated your model, make sure
the
units of each
equation are consistent.
Hand in your final documented Vensim model file (.mdl file).
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