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From: Bruno Luong on 16 Mar 2010 03:52
"Ibraheem " <ibr_ex(a)hotmail.com> wrote in message <hnmql4$osg$1(a)fred.mathworks.com>...
> Hi Bruno,
> >http://www.mathworks.com/matlabcentral/newsreader/view_thread/260308#679215
> > replace "w'*x" by kernel operator applied on w and x.
> Thank you again for your concern and quick reply.
> I have read your post but I can not understand the notation.
> Do you mean :
> W = sum( lambda*Y*X);
> b = -1/2 ( mean (SV(SV(2)<0)) W'*X + mean(SV(SV(2)>0)) W'*X);

> I don't understand two things:
> 1. Does the mean for all matrix or for the second column only.

For a data #i, Yi is class (or group +/--1) of the data Xi (a vector observation in R^n, its is one row of the training data your pass to svmclassify), and lambda_i is the dual variable (scalar) returned. Multiply these three term and add them together (sum on i), you get a vector W. Next compute b which is a scalar.

> 2. What is the dual variable ? Is it alpha ?
> Sorry for bothering and regards,

Matlab classify returns in Alpha the product (Yi*lambdai_i) after training.

Bruno
From: Ibraheem on 16 Mar 2010 19:34
I think I get the idea now, thank you very much.
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