On Sun, Mar 18, 2012 at 12:22 PM, Andreas <[email protected]> wrote: > On 03/18/2012 05:07 PM, James Bergstra wrote: >> On Sat, Mar 17, 2012 at 11:55 PM, Mathieu Blondel<[email protected]> >> wrote: >> >>>> The alpha specified this way could (should?) have the same name and >>>> interpretation as the l2_regularization coefficient in the >>>> SGDClassifier. >>>> >>> Would you convert alpha into a C internal value or would you patch >>> libsvm / liblinear to use alpha? I don't understand how the former >>> would be different from the scale_C option, in practice. >>> >> In the implementation, I would convert it to C and call libsvm >> similarly to how scale_C is working now. The reason that I piped up on >> the list was purely for code readability. If I read >> >> svm = SVC(C=10) >> >> it really looks like svm is an SVM model with C=10. If there's a >> implicit scale_C=True in the arguments, it's confusing. This caused >> my code to have a bug, and I got annoyed. >> >> On the other hand if I had read >> >> svm = SVC(alpha=1e-3) >> >> then I would have wondered "what's alpha?" and gone to look up the >> docs and learn how alpha is converted to C. >> > I see two possible remedies: > - Having two different possible parameters, as James and I > proposed earlier (and which Lars didn't seem to like much), > where the user can specify either "C" or "alpha" > > - Changing the "scale_C" option back to "False" by default. > That means having different parameter names than other > linear models and "inconsistent" cross-validation. > > Are there any other options? >
Another minor variation: make a second libsvm wrapper constructor that only uses alpha, never C. e.g.: svm = SVCa(1e-3) ------------------------------------------------------------------------------ This SF email is sponsosred by: Try Windows Azure free for 90 days Click Here http://p.sf.net/sfu/sfd2d-msazure _______________________________________________ Scikit-learn-general mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/scikit-learn-general
