一类非线性方程极限环的存在性

THE EXISTENOE OF LIMITING CYCLE OF A CLASS OF NONLINEAR DIFFERENTIAL EQUATION

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In this paper,an existence theorem of limiting cycle of the system of equations (dx)/(dt)=φ(y)-F(x) (dy)/(dt)=-g(x)(E) is proved,where φ(y)is not assumed to be monotonic,and the tradition- al condition“|φ(±∞)|=+∞”is weakened. theorem is a special case of this theorem,when φ(y)=y.