hi Ian, yes you're right, however the dev version should be up to date:
http://scikit-learn.org/dev/modules/svm.html#svc see note on scale_C parameter. Alex On Tue, Feb 14, 2012 at 10:49 PM, Ian Goodfellow <[email protected]> wrote: > This page says that SVC minimizes > sum(square(w)) + C * sum(margins) > > I believe it actually minimizes > sum(square(w)) + C * mean(margins) > > This may seem like a pedantic distinction but it's very important for > being able to compare sklearn to other svm implementations. > > Am I correct that SVC minimizes the mean rather than the sum of the > margins? If so the doc should be updated. > > The following script demonstrates that fitting two copies of X and y > with C=1 is equivalent to fitting just X,y with C=1 and is not > equivalent to fitting X,y with C=2. If SVC followed the doc we would > expect the opposite result in both cases. > > > > > import numpy as np > rng = np.random.RandomState([1,2,3]) > from sklearn.svm import SVC > > svm_type = SVC(kernel = 'linear', C = 1.) > > > X = rng.randn(100,5) > > W = rng.randn(5,5) > > y = np.dot(X,W).argmax(axis=1) > > > print 'fitting svm 1' > svm1 = svm_type.fit(X,y) > > print 'fitting svm 2' > svm2 = svm_type.fit(np.concatenate([X,X],axis=0), > np.concatenate([y,y],axis=0)) > > idiff = np.abs(svm1.intercept_-svm2.intercept_).max() > > wdiff = np.abs(svm1.coef_-svm2.coef_).max() > > print max(idiff,wdiff) > > > svm3 = SVC(kernel = 'linear', C = 2.).fit(X,y) > > print np.abs(svm1.intercept_-svm3.intercept_).max() > > ------------------------------------------------------------------------------ > Keep Your Developer Skills Current with LearnDevNow! > The most comprehensive online learning library for Microsoft developers > is just $99.99! Visual Studio, SharePoint, SQL - plus HTML5, CSS3, MVC3, > Metro Style Apps, more. Free future releases when you subscribe now! > http://p.sf.net/sfu/learndevnow-d2d > _______________________________________________ > Scikit-learn-general mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/scikit-learn-general ------------------------------------------------------------------------------ Keep Your Developer Skills Current with LearnDevNow! The most comprehensive online learning library for Microsoft developers is just $99.99! Visual Studio, SharePoint, SQL - plus HTML5, CSS3, MVC3, Metro Style Apps, more. Free future releases when you subscribe now! http://p.sf.net/sfu/learndevnow-d2d _______________________________________________ Scikit-learn-general mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/scikit-learn-general
