= Real Ginzburg–Landau equation
{title2=$A_T=rA+\xi A_{XX}-g|A|^2A$}
The real-coefficient Ginzburg–Landau <amplitude equation> has complex $A$ and real parameters, usually $\xi,g>0$ near a supercritical stationary pattern onset. A detuned plane wave $A=\rho e^{iQX}$ has $\rho^2=(r-\xi Q^2)/g$. Its phase and amplitude sidebands determine the narrower <Eckhaus instability> stability band. It is a local envelope model; additional conserved fields or mean flows may need their own equations.
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