From jpretti@barrow.uwaterloo.ca Wed Jan 28 09:19:04 1998
Date: Tue, 27 Jan 1998 09:57:05 -0500 (EST)
From: John-Paul Pretti <jpretti@barrow.uwaterloo.ca>
To: hwolkowi@orion.math.uwaterloo.ca
Subject: Assignment 1 Comments to C&O 370 Students


Each question was worth 10 marks. Q2 and Q3 were only checked to ensure
they were handed in. Q1 and Q3 were marked in detail.

Comments On Question 1.

- most students lost 1 mark for not forcing the variables to be
integer-valued

- some also lost a mark for omitting the nonnegativity constraints 

- the most common mistake was omitting the waste from excess smaller rolls
as alluded to in the hint; this should have been incorporated into the
objective function (-2 marks)

- an additional mark was lost by students who used equality as opposed to
inequality constraints; this incorrectly narrows the feasible region

- only 1 mark was deducted for students who included (up to 9) unnecessary
'cutting' combinations (e.g. one roll of 24 and one of 32); the hint said
to simplify the problem by cutting each roll up as much as possible

- a couple marks were deducted for omitting combinations 

Comments on Question 4

a) This question was done well. Note that very little detail was required.

b) Only several students got this question. It was a simple matter of
looking at the shadow price of manganese. One way of looking at it is to
view the production of manganese as a new activity. Alternatively, one
might view it as requiring one extra unit of manganese. 

c) Fairly well done. But be careful when extracting a valid range for a
variable (i.e. -0.05 >= -0.5).

d) Also done fairly well. Don't forget to read the question - what are the
values of the other basic variables when this happens ?!?

e) Done perfectly.

Please see me if you have any comments or questions.

John-Paul Pretti (J.P.) 
University of Waterloo
Department of Combinatorics & Optimization
MC 5136A (519)888-4567 x6895