On Mon, Mar 25, 2013 at 9:19 PM, Andreas Mueller
<amuel...@ais.uni-bonn.de> wrote:

> I'm confused. Since when is that so? The other losses definitely support
> OvR multi-class. I would be quite surprised if 'log' does not.

predict_proba currently raises an exception in the multiclass case:
https://github.com/scikit-learn/scikit-learn/blob/master/sklearn/linear_model/stochastic_gradient.py#L676

We can modifiy predict_proba so that it computes the probabilities of
each one-vs-rest task and then normalize them, like we already do
here:
https://github.com/scikit-learn/scikit-learn/blob/master/sklearn/multiclass.py#L111

I'm not sure if there exists any strong theoretical motivation for
doing this normalization but at least this is how liblinear is doing
it and this is also the method recommended by this paper:
http://www.research.ibm.com/people/z/zadrozny/kdd2002-Transf.pdf

Mathieu

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