凡·德·波尔方程极限环的存在性

Existence of limited loop for van der pol equations

改进了凡·德·波耳的有关工作，利用等倾线给出了另一种证明方法，给出了极限环稳定性的判断．

This paper improves the work of van der pol. Give another kind means of prove for using equal tilt thread. Give judgment of stable quality of limited loop.