Stokes line ($\mathrm{Im}(S_1-S_2)=0$)

With the convention used here, a Stokes line is a ray where competing exponential actions have the same imaginary part. A subdominant exponential can acquire a rapidly changing multiplier there. For $e^{\pm x^2/\epsilon }$, these rays have $\arg x=m\pi /2$. The anti-Stokes lines instead have equal exponential magnitudes.