Question 11
 

I have used LIBSVM; the answer that I get is one of a) to d) if I scale it appropriately. However, if I scale it, the margin in the transformed domain is not any more +/-1 at the support vectors. So technically the answer proposed is right (since it separates the points with a maximum margin) but it doesn't satisfy the requirement that the margins be +/- 1 at the support vectors.

Re: Question 12
 

Just to make sure, this is a double-check on the answer as the question asks explicitly for a geometric solution. Right?

Re: Question 12
 

Correct. I did it with LIBSVM though :D. I have verified that the libsvm solution provides margins equal to 1 for the support vectors. By scaling it via a positive constant I get one of the four.

Thanks,

Fernando.

Re: Question 12
 

LIBSVM is getting popular :). Someone even applied it to the puzzle from Lecture 1 if you remember that.

http://book.caltech.edu/bookforum/sh...21&postcount=6

Re: Question 12
 

I guess that given that we have libsvm, my lazy inside refused to do sit down and write the problem on paper :D.

Re: Question 12
 

Geometrically, it is clear to see what the values of the weights and b should be. My results using a geometric approach match the results I get using Octave implemenation of SVM. Of course, libsvm also confirms my results as it always has the final say :) in matters related to SVM :).

Re: Question 12
 

It seems like the original question was never answered.

Geometrically, one can find a w1, w2, and b which define the separating plane. Clearly you get the same plane if you multiply w1, w2, and b by some constant A. In the SVM formalism A was fixed so that w.z+b=1 at the nearest positive point.

Do we need to
-choose the w1, w2, and b which define the correct plane AND have the correct A, or
-is it sufficient to choose one of the infinitely many w1, w2, and b which define the correct plane without necessarily having the correct normalization A?

It's also possible that the correct answer has the correct normalization and I've made some mistake.

Re: Question 12
 

It is the latter, with no normalization needed. Since the wording of the problem asks for what values specify the plane, a set of values that does specify the plane would be the correct answer and if none of them does then it's none of the above.

Re: Question 12
 

Great - looking back I agree that the question wording is unambiguous, though perhaps for this problem the graph of P(getting the right answer) vs Carefulness is non-monotonic. Thank you!

Re: Question 12
 

:)