Further to my last message, there seems to be a rather serious regression in 
OneVsRestClassifier in git master. I didn't find an issue about it.

The following reproduces the behaviour in question:



import numpy as np
import sklearn
from sklearn.multiclass import OneVsRestClassifier
import sklearn.svm as svm
rng = np.random.seed(0)
train = np.random.randn(1000, 400)                                              
train_l = np.random.random_integers(1, 10, size=(1000,))
test = np.random.randn(1000, 400)
test_l = np.random.random_integers(1, 10, size=(1000,))
svm = OneVsRestClassifier(svm.SVC(C=0.01, scale_C=False)).fit(train, train_l)
print "Training accuracy:", (train_l ≡ svm.predict(train)).mean()
print "Test accuracy:", (test_l ≡ svm.predict(test)).mean()
print "scikit-learn version:", sklearn.__version__




wardefar@atchoum:~$ python test.py
/u/wardefar/.local/lib/python2.7/site-packages/scikit_learn-0.10-py2.7-linux-x86_64.egg/sklearn/svm/classes.py:184:
FutureWarning: SVM: scale_C will be True by default in scikit-learn 0.11
  cache_size, scale_C)
Training accuracy: 1.0
Test accuracy: 0.096
scikit-learn version: 0.10


wardefar@atchoum:~$ python test.py
/u/wardefar/.local/lib/python2.7/site-packages/scikit_learn-0.11_git-py2.7-linux-x86_64.egg/sklearn/svm/classes.py:228:
FutureWarning: SVM: scale_C will disappear and be assumed to be True in
scikit-learn 0.12
  cache_size, scale_C, sparse="auto")
Training accuracy: 0.0
Test accuracy: 0.107
scikit-learn version: 0.11-git



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