= Spatiotemporal wave-packet stability
The response to a localized perturbation must be followed in space as well as time. Growth at a fixed position is <absolute wave-packet instability>; growth transported away while the original position decays is <convective wave-packet instability>. The <Briggs-Bers criterion> evaluates the relevant complex spatial branches of a <dispersion relation>, while a real-wavenumber temporal mode test alone does not generally distinguish those behaviors.
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