tanotes5

# tanotes5 - back properly (i.e. using (0 ,,-1 , 1) 1 or (0 ,...

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CO 350 Linear Optimization (Spring 2009) TA’s comments for Assignment 5 Q1: (a) (2 marks) Most students got this. Some included the extra pairs ( x 5 ,x 3 ) and ( x 5 ,x 6 ). This would get you 0/2 even if you did include the correct pairs. it’s 11 weeks into the term and you should know better than doing an invalid pivot on the simplex method. (b) (4 marks) Mostly well done, although some students demonstrated poor understanding of the lexicographic simplex method (e.g. assuming the current matrix is always the identity). Also, some students came up with the correct vectors to compare but failed to pick the lexicographically minimum one (e.g. implicitly, or in some cases explicitly, claiming that min { 1 2 , - 1 , - 2 } = 1 2 ). (c) (4 marks) Many students did not substitute
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Unformatted text preview: back properly (i.e. using (0 ,,-1 , 1) 1 or (0 , 1 ,-1 , 1) to compare against (0 , 2 , 1 , 0) 2 and (0 , 2 ,-4 , 0) 2 ). Also, some students arrived at the condition that x 6 enters if-1 &lt;-2, and then multiplied both sides by and concluded that &lt; 1 2 . However, the multiplication step implicitly assumes that &gt; 0, which in this case you can ( and need to ) assume, because if 0, ( x 4 ,x 6 ) would have been an invalid pivot. Finally, technically, one needs to verify the case when = 1 2 and the 3rd entry in (0 , 2 ,-4 , 0) 2 and (0 , 1 2 ,-1 , 1 2 are tied (which a handful of you did). However, those who neglected to do this was not penalized. 1...
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