单位根检验
import statsmodels.tsa.stattools as ts
from datetime import datetime
import pandas_datareader.date as web
amzn = web.DataReader('AMZN','quandl',datetime(2005,1,1),datetime(2015,1,1))
ts.adfuller(amzn['AdjClose', 1])
主要用于检查常差是否是均值回复的