2013/9/25 Luca Cerone <luca.cer...@gmail.com>: > This morning I checked the source for LogisticRegression in > sklearn/linear_model/logistic.py and realized that by default it performs > multiclass classification > (this is not explained in the user guide > http://scikit-learn.org/stable/modules/linear_model.html#logistic-regression, > though).
All our classifiers support multiclass classification and this is documented in various places. > There are still a few things that are not clear to me from the > documentation. Can you customize the classifier to perform a different > decision function? You can subclass it and override the decision_function method. > Or can I "hook" a preprocessing step to be applied to the data (I am > thinking for example for polynomial logistic regression, where from the > original dataset You can implement a polynomial expansion as a transformer object, then tie it to logistic regression using a sklearn.pipeline.Pipeline. See the developer's docs, esp. the "Rolling your own estimator" guide [1], or our recent paper [2] for the conventions. > 1. can I use a norm different from l1 or l2? For what? > 2. similarly, can I define my own cost function? No, unless you hack the source code. > 3. can I try alternative optimization algorithms? You can try SGDClassifier(loss="log") which also implements one-vs.-all logistic regression, but trained with stochastic gradient descent. [1] http://scikit-learn.org/stable/developers/index.html#rolling-your-own-estimator [2] http://staff.science.uva.nl/~buitinck/papers/scikit-learn-api.pdf ------------------------------------------------------------------------------ October Webinars: Code for Performance Free Intel webinars can help you accelerate application performance. Explore tips for MPI, OpenMP, advanced profiling, and more. Get the most from the latest Intel processors and coprocessors. See abstracts and register > http://pubads.g.doubleclick.net/gampad/clk?id=60133471&iu=/4140/ostg.clktrk _______________________________________________ Scikit-learn-general mailing list Scikit-learn-general@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/scikit-learn-general
