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"""
==============
Non-linear SVM
==============
Perform binary classification using non-linear SVC
with RBF kernel. The target to predict is a XOR of the
inputs.
The color map illustrates the decision function learn by the SVC.
"""
print __doc__
import numpy as np
import pylab as pl
from sklearn import svm
xx, yy = np.meshgrid(np.linspace(-3, 3, 500),
np.linspace(-3, 3, 500))
np.random.seed(0)
X = np.random.randn(300, 2)
Y = np.logical_xor(X[:, 0] > 0, X[:, 1] > 0)
# fit the model
clf = svm.NuSVC()
clf.fit(X, Y)
# plot the decision function for each datapoint on the grid
Z = clf.decision_function(np.c_[xx.ravel(), yy.ravel()])
Z = Z.reshape(xx.shape)
pl.imshow(Z, interpolation='nearest',
extent=(xx.min(), xx.max(), yy.min(), yy.max()),
aspect='auto', origin='lower', cmap=pl.cm.PuOr_r)
contours = pl.contour(xx, yy, Z, levels=[0], linewidths=2,
linetypes='--')
pl.scatter(X[:, 0], X[:, 1], s=30, c=Y, cmap=pl.cm.Paired)
pl.xticks(())
pl.yticks(())
pl.axis([-3, 3, -3, 3])
pl.show()
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