为了避免你的胡说八道误导小同学,把这个事情再完整澄清一下:
wiki上平稳的定义:In mathematics and statistics, a stationary process (or strict(ly) stationary process or strong(ly) stationary process) is a stochastic process whose joint probability distribution does not change when shifted in time. Consequently, parameters such as the mean and variance, if they are present, also do not change over time and do not follow any trends.
你给的链接里平稳的定义:A stochastic process (a collection of random variables ordered in time) is said to be (weakly) stationary if its mean and variance are constant over time, i.e. time invariant. By contrast, a nonstationary time series will have a time-varying mean or a time-varying variance
or both.
无论哪个定义,显然一般地定义平稳不需要用密度函数,而是要用joint probability distribution 或分布参数(即数字特征)定义。至于你以前帖子里说的“ joint probability distribution 不确定,需要用密度函数”完全是撒谎,如果密度函数能确定, joint probability distribution也必然是确定的。
劝你一句,无知不可怕,不要脸才可怕。明知自己无知还故意胡说八道,太low了。你就算骗得了几个网上围观的小朋友,骗得了你自己良心?当然,如果你没良心,算我白说了。
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