= Quasistatic vertical-field magnetoconvection
{title2=$R_c=\frac{s(s^2+Q\pi^2)}{\alpha^2},\quad s=\alpha^2+\pi^2$}
When the magnetic field supplies instantaneous damping rather than an evolving magnetic perturbation, the roll amplitudes obey a two-variable linear system with <trace> $-[s+\sigma(s+Q\pi^2/s)]<0$. Its <determinant> vanishes at the displayed stationary threshold. Therefore its initial instability cannot be a <Hopf bifurcation>. This reduced model must not be confused with a three-variable magnetoconvection model carrying finite magnetic diffusivity and an additional oscillatory mode.
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