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From: Amaradonna
Subject: GPSS
Date: Sun, 27 Oct 2002 08:40:59 EST

A few of us graduates here have been trying to solve a GPSS (general purpose simulation software) problem, however as there is no results page for us to compare our solutions, I was wondering whether it maybe possible to have some feedback to what we are trying to resolve, below.

Thank you very much in advance and I look forward to hearing from you soon.




A barber's shop in Watford is a one-man operation open from 8am to 5pm each

day. Customers arrive throughout the day and the inter-arrival times (in
minutes) between customers is 20 minutes ± 5 minutes. This is a uniformly
distribution using only integer values. The service time at the shop is
similarly distributed over 23 minutes ± 10 minutes.

A.  Write a GPSS program that simulates operation of the shop over a 9 hour

day. Explain briefly each line of your program.

B.  Suppose that 85% of the customers who arrive at the shop need only a
haircut and the remaining 15% require both a haircut and a shave. Assume
the haircuts take 20 minutes (± 7 mins, uniformly distributed) and shaves
take 20minutes (± 5 minutes, uniformly distributed). Modify your GPSS
to reflect these changes, run it and comment on the results.

C.  Now suppose that the inter-arrival patterns of the two types of
described in part B are known to be 18 ± 5 minutes for those customers who
only need a haircut and 102 ± 30 minutes for customers requiring both a
haircut and a shave. Modify your GPSS program to reflect these changes, run

the program and comment on the results.

Exercise 4

An old people's home has an in-house surgery which is staffed by a single
and three specialists. Sixty percent of the patients who request help can
dealt with by the GP, the remaining 40% of the patients require access to
of the specialists. Assume:

·   The time between successive patient arrivals is in the range 22 ± 12
·   Patients who do not need a specialist require 22 ± 15 minutes of the
time; those who require a specialist take 5 ± 3 minutes of the GP's time,
wait 30 ± 20 minutes for a specialist to arrive, then spend 45 ± 20 minutes

with the specialist.

1. Do a simulation study of the operation of this surgery which opens for
business from 9am to 5pm every day, to determine:

a.  How busy is:

i.  the GP (i.e. what portion of the time is the GP with a patient?) and
ii. a specialist.

a.  What is the average waiting time to wait to see:
i.  the GP and (ii) a specialist?

a.  How many patients can be seen in one day by:

(i) the GP and (ii) the specialists.

2.  10% of the patients who are classified as not needing a specialist,
revisit the GP after they have left the consulting room but not the
Modify your program and comment on your simulation report. How will your
answers for part (1) change?

3. Consider the original problem in part (1), 2% of patients are VIPs (Very

Important Persons) who are seen immediately by the GP, pre-empting any
patient that might be with the GP at that time. The GP only spends 2
with a VIP, and then resumes attending to the pre-empted client. VIP's are
not referred to a specialist and hence leave the surgery after seeing the
consultant. Modify your program to accommodate this change and comment on
your simulation report. On a daily basis what is the average time spent
attending to VIPs?

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