Unformatted text preview: example the product of (2 , 1) and (1 , 1) T is 1. The same way, if the problem Ax = b,x ≥ 0 is infeasible for some b ≥ 0, it does not mean A < 0. There are lots of other cases when the matrix is positive, or neither positive nor negative, and the problem is infeasible. Also, some of you used v > 0 without explaining if they mean that EVERY coordinate of v is positive, or that AT LEAST ONE coordinate is. I did not penalize this, but next time be more careful.Working with vectors is sometimes more complicated than working with numbers, but if you’re not sure if you can generalize some statement, think about a 2dimensional case ﬁrst. 1...
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 Fall '08
 TODD
 Addition, 2dimensional case ﬁrst

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