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ladybird2012 06-06-2012 03:00 PM

Question 14 - bias term
 
For Question 15 we implement the RBF model, and there is a bias term to be calculated. It seems to me that there are two ways of going about this:

1) use a similar logic to what we had for linear regression. This seems to be what is suggested on slide 15 of lecture 16 (RBF network slide).

2) in the RBF notes it's mentioned in the footnote on page 27 that the bias = mean(y).

I implemented both and get different values for the bias as well as for Eout. I was wondering if anyone had tried both methods and come up with consistent values (i.e., I have a bug that I haven't managed to find despite looking hard and long) or if there is a reason to pick one method over the other.:clueless:

Also while I'm at it, shouldn't the last line of the footnote only refer to w since the centers are chosen in an unsupervised way?

yaser 06-06-2012 03:04 PM

Re: Question 15 - bias term
 
Quote:

Originally Posted by ladybird2012 (Post 2815)
For Question 15 we implement the RBF model, and there is a bias term to be calculated. It seems to me that there are two ways of going about this:

1) use a similar logic to what we had for linear regression. This seems to be what is suggested on slide 15 of lecture 16 (RBF network slide).

This is the correct way. Treat b as you treated w_0 in linear regression. The only reason it's called b here is not to conflict with the SVM kernel version.

itooam 09-05-2012 02:22 PM

Re: Question 15 - bias term
 
TTT (To The Top) Useful to know :)

DavidNJ 09-17-2012 02:51 AM

Re: Question 15 - bias term
 
What is the bias term in a linear regression? Aren't they solved as the pseudo inverse: inv(x'*x)*x'*y?

yaser 09-17-2012 08:39 AM

Re: Question 15 - bias term
 
Quote:

Originally Posted by DavidNJ (Post 5397)
What is the bias term in a linear regression? Aren't they solved as the pseudo inverse: inv(x'*x)*x'*y?

It is w_0 in our notation, corresponding to x_0=1 which is the first column of the matrix {\rm X} that is used in the pseudo-inverse.


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