= Fold and Hopf thresholds of a directly forced cubic amplitude
{title2=$\Lambda_{\rm cusp}=\sqrt3/2,\quad\Lambda_{\rm H,min}=2^{-1/3}$}
For the <directly forced cubic amplitude equation>, a <saddle-node bifurcation> requires $\Lambda^2=1/s-1/(4s^4)$ and $\mu=s+1/(2s^2)$. The right side has its unique maximum $3/4$ at $s=1$, giving a <cusp bifurcation> at $(\Lambda,\mu,s)=(\sqrt3/2,3/2,1)$. The <stability matrix> has <trace> $2(\mu-2s)$ and <determinant> $(\mu-3s)(\mu-s)+\Lambda^2$. A <Hopf bifurcation> requires $\mu=2s$, $s(s^2+\Lambda^2)=1$ and $\Lambda^2-s^2>0$. These imply $\Lambda>2^{-1/3}$; equality is a double-zero linear degeneracy rather than an ordinary <Hopf bifurcation>.
Back to article page
