关于快速多级子的使用方法大家可能还不是很熟悉，这里面详细介绍了其基本原理和使用方法，以及其自身的限制-Son of rapid multi-level approach we use may not be familiar, there is described in detail the basic principles and use, and its own limitations

an open MLFMM code,very useful for CEM beginners!