scikit学习示例中的decision_function

Question

我听不懂代码。它在做什么？

clf.decision_function([[1]])

我读了scikit-learn.org，但听不懂。

X = [[0], [1], [2], [3]]
Y = [0, 1, 2, 3]
clf = svm.SVC(gamma='scale', decision_function_shape='ovo')
clf.fit(X, Y) 
SVC(C=1.0, cache_size=200, class_weight=None, coef0=0.0,
    decision_function_shape='ovo', degree=3, gamma='scale', kernel='rbf',
    max_iter=-1, probability=False, random_state=None, shrinking=True,
    tol=0.001, verbose=False)
dec = clf.decision_function([[1]])
dec.shape[1] # 4 classes: 4*3/2 = 6
6
clf.decision_function_shape = "ovr"
dec = clf.decision_function([[1]])
dec.shape[1] # 4 classes
4