Newell-Whitehead-Segel amplitude equation: A_T = A - |A|^2 A (complex Ginzburg-Landau onset)

Newell-Whitehead-Segel amplitude-equation framework (NWS 1969 J Fluid Mech 38, 279). Setup: weakly nonlinear reaction-diffusion / convection system near Turing onset r = epsilon^2 where a band of unstable wavenumbers centered at q_c…