本征正交分解（POD）是以能量表述的随机场的最优分解，采用瑞利商概念及其极值性质推导了POD原理，可用于瞬态场的本征正交分解，代码有注释说明(Proper orthogonal decomposition (POD) is the optimal decomposition of the random field expressed by energy. The principle of POD is deduced by the Rayleigh concept and its extreme value. It can be used for the Proper orthogonal decomposition of the transient field. The code has a commentary)