Wronskian flux (source code)

= Wronskian flux
{c}
{title2=$\mathcal J=\operatorname{Im}(E^*E')$}

For $E''+k^2(x)E=0$ with real $k^2$, differentiation gives $\mathcal J'=\operatorname{Im}(E^*E'')=0$. This conserved <Wronskian> measures directed <wave> flux. In a one-dimensional <ordinary plasma wave>, the mean <Poynting flux> is $c^2\mathcal J/(8\pi\omega)$ in <Gaussian units>. It proves $R+T=1$ for a lossless two-channel scattering problem.