polynomial expansion
for i in 0..power for p in 0..i: output x1^(i-p) * x2^p
#特征映射函数
def feature_mapping(x1,x2,power):
data = {"f{}{}".format(i - p,p): np.power(x1,i - p)*np.power(x2,p)
for i in np.arange(power + 1)
for p in np.arange(i + 1)
}
return pd.DataFrame(data)
#把特征映射到 power = 3
data = feature_mapping(x1, x2, power=3)
