In the paper, we give an existence theorem of periodic solution for Liénard equation $\dot{x}=y-F(x)$, $\dot{y}=-g(x)$. As a result, we estimate the amplitude $\rho (\mu )$ (maximal $x$-value) of the limit cycle of the van der Pol equation $\dot{x}=y-\mu (x^3/3-x)$, $\dot{y}=-x$ from above by $\rho (\mu )<2.3439$ for every $\mu \ne 0$. The result is an improvement of the author’s previous estimation $\rho (\mu )<2.5425$.
@article{107715, author = {Kenzi Odani}, title = {On the limit cycle of the Li\'enard equation}, journal = {Archivum Mathematicum}, volume = {036}, year = {2000}, pages = {25-31}, zbl = {1048.34067}, mrnumber = {1751611}, language = {en}, url = {http://dml.mathdoc.fr/item/107715} }
Odani, Kenzi. On the limit cycle of the Liénard equation. Archivum Mathematicum, Tome 036 (2000) pp. 25-31. http://gdmltest.u-ga.fr/item/107715/
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