PERIODIC SOLUTIONS FOR A SINGULAR LIENARD EQUATION WITH INDEFINITE WEIGHT

In this paper, the existence of positive periodic solutions is studied for a singular Lienard equation where the weight function has an indefinite sign. Due to the lack of a priori estimates over the set of all possible positive periodic solutions in this equation, a new method is proposed for estimating a priori bounds of positive periodic solutions. By the use of a continuation theorem of the Mawhin coincidence degree, new conditions for existence of positive periodic solutions to the equation are obtained. The main results show that the singularity of coefficient function associated to the friction term at x = 0 may help the existence of periodic solutions.