From the marker - W08:

Here are some commonly made mistakes and comments on Assignment 1:

2.1.1) ||x|| is not differentiable at x=0.
2.1.2 ) The question was for a general function g, not g = ||x||.
3.1 a,b,c) The boundary must include the conditions x1, x2 >= 0, not
just x1 = 0 or x2 = 0.
3.1 d) The boundary of R^n is the empty set.
3.1 e) This set is empty.
3.2 a,b) Many skipped this question. If you would like help with
topological ideas, please feel free to see Prof. Wolkowicz or Jamie
(the TA) for help. Otherwise, this question was done quite well.
4.1.2 ) 0 is never an eigenvector. But, 0 is part of the eigenspace,
so sometimes this causes confusion.
4.1.3) To get full marks, you need to perform sufficient elementary
operations to show that p=0 is the value (and only value) that
minimizes the rank.