说明：  鉴于求matlab版本的Penman-Montieth方程未果，本人编写了程序，其中a,b取值是黄土高原适合的值，可以自己调整。步骤明了，简单易懂
(View of the demand matlab version of the Penman-Montieth equation unsuccessful, I write a program, where a, b value is the value of the Loess Plateau suitable, you can make their own adjustments. Steps to understand, easy to understand)