The Ginzburg–Landau equation, named after Vitaly Ginzburg and Lev Landau, describes the nonlinear evolution of small disturbances near a finite wavelength bifurcation from a stable to an unstable state of a system. At the onset of finite wavelength bifurcation, the system becomes unstable for a critical wavenumber k c which is non-zero. In the neighbourhood of this bifurcation, the evolution of disturbances is characterised by the particular Fourier mode for k c with slowly varying amplitude A (more precisely the real part of A ). The Ginzburg–Landau equation is the governing equation for A . The unstable modes can either be non-oscillatory (stationary) or oscillatory.