I had a question about Question 16 of the exam about the existence of a subgradient. I saw in the solution that you've considered cases where a > 1 and a = 1, but what about when a < 1. In that case wouldn't there be more than one subgradient? I'm not sure if this has been asked before.
But I think the formulation of the answer for me was a bit confusing. It's true that for a = 1, we have a unique subgradient but for a < 1 we have more than one subgradient and hence it is not unique. That's why I answered 'if a subgradient exists then it is not unique', and I thought it encapsulated more the fact that it all depends on a.
I remember asking a TA about this because I was hesitating between the two answers and he said to answer as I understood it.
Yes, I marked the same option "If a subgradient exists then it is not unique". I also considered the fact that it depends on 'a', and for a<1 we have more than one subgradient hence it is not unique.
yes but the question clearly states that the value a is arbitrary. given that, you have to ask if any box can be ticked (answer must be always correct, as usual in MC questions)
Q16 Subgradients
Hello,
I had a question about Question 16 of the exam about the existence of a subgradient. I saw in the solution that you've considered cases where a > 1 and a = 1, but what about when a < 1. In that case wouldn't there be more than one subgradient? I'm not sure if this has been asked before.
Thanks in advance
yes you're correct. in that case the subgradient is not unique.
was that your question?
2
Yes! Thank you for the quick answer.
But I think the formulation of the answer for me was a bit confusing. It's true that for a = 1, we have a unique subgradient but for a < 1 we have more than one subgradient and hence it is not unique. That's why I answered 'if a subgradient exists then it is not unique', and I thought it encapsulated more the fact that it all depends on a.
I remember asking a TA about this because I was hesitating between the two answers and he said to answer as I understood it.
It'd be nice to know if someone else had this confusion.
1
Yes, I marked the same option "If a subgradient exists then it is not unique". I also considered the fact that it depends on 'a', and for a<1 we have more than one subgradient hence it is not unique.
Me too
Same for me !
yes but the question clearly states that the value a is arbitrary. given that, you have to ask if any box can be ticked (answer must be always correct, as usual in MC questions)
1
Yes I see now. Thanks for the answer.
This kind of question can get very confusing very quickly, and unfortunately you can't explain your answers in MC.
Honestly, it still hurts losing points over questions like this one when you're so sure of the answer.
1
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