= Spatially forced convection amplitude equation
{title2=$A_T=\mu A+\beta\overline A-\lambda|A|^2A$}
A steady spatial forcing at twice the critical <wavenumber> permits coupling of the negative critical <Fourier mode> to the positive critical mode. A <weakly nonlinear expansion> then permits a term $\beta\overline A$ in the <Landau amplitude equation>. Its coefficient is found by projecting the resonant forcing-advection terms onto the <adjoint eigenfunction>. Reflection-symmetric forcing permits real coefficients. The <symmetry> permission does not prove a nonzero coefficient: it can vanish for a particular model or mode structure.
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