= Outer-edge source of a viscous disk
{title2=$\bar\nu\Sigma=\frac{\dot M}{3\pi}(1-\sqrt{r_1/r})$}
A narrow <surface density of a disk> source approaching the outer edge from inside, with $S=S_0\delta(r-r_2)$ normalized to have full weight, gives $\dot M=2\pi r_2S_0$ and the displayed steady interior profile. This follows by replacing the inner source integral by $r_2S_0$ and integrating $u^{-1/2}$. The flux jumps from $\dot M$ just inside to zero outside the injecting edge. Thus a zero exterior flux is consistent, whereas a continuous zero interior boundary trace is not. A half-weight convention for a symmetric endpoint <Dirac delta function> represents a different total injected mass; it must not be silently mixed with the full-weight boundary source.
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