特征值，特征向量排序

import numpy as np

evals=np.array([0,2,5,3,1])
evecs=np.array([[1,1],[2,3],[4,5],[7,7],[6,8]])
print evecs.shape
# 默认按升序排列
sorted_indices = np.argsort(evals)
# 取相反数 变为按降序排列
sorted_indices = np.argsort(-evals)
print sorted_indices
k=3
# 切片取特征向量列向量
topk_evecs = evecs.T[:,sorted_indices[:k]]
print topk_evecs