我正在尝试跟随Abdi和Williams-主成分分析(2010)并通过SVD构建主成分,使用numpy.linalg.svd
。
当我显示经过sklearn拟合的PCA的components_
属性时,它们与我手动计算的完全相同,但是一些(而不是全部)的符号相反。这是什么原因?
更新: 我下面的(部分)答案包含了一些额外的信息。
取以下示例数据:
from pandas_datareader.data import DataReader as dr
import numpy as np
from sklearn.decomposition import PCA
from sklearn.preprocessing import scale
# sample data - shape (20, 3), each column standardized to N~(0,1)
rates = scale(dr(['DGS5', 'DGS10', 'DGS30'], 'fred',
start='2017-01-01', end='2017-02-01').pct_change().dropna())
# with sklearn PCA:
pca = PCA().fit(rates)
print(pca.components_)
[[-0.58365629 -0.58614003 -0.56194768]
[-0.43328092 -0.36048659 0.82602486]
[-0.68674084 0.72559581 -0.04356302]]
# compare to the manual method via SVD:
u, s, Vh = np.linalg.svd(np.asmatrix(rates), full_matrices=False)
print(Vh)
[[ 0.58365629 0.58614003 0.56194768]
[ 0.43328092 0.36048659 -0.82602486]
[-0.68674084 0.72559581 -0.04356302]]
# odd: some, but not all signs reversed
print(np.isclose(Vh, -1 * pca.components_))
[[ True True True]
[ True True True]
[False False False]]