Complex wavenumber
= Complex wavenumber
{title2=$K$}
A <complex number> used as a <wavenumber> to encode both spatial oscillation and exponential variation of a <wave amplitude>. With the convention $e^{i\omega t-iKx}$, a disturbance decaying for increasing $x$ has $\operatorname{Im}K<0$. The sign depends on the convention; <thermal diffusion waves> provide a concrete example.