= Robin spectral determinant for defocusing NLS
{c}
{title2=$\mathcal D(k)=(2k+ic)a(k)a^\sharp(-k)+(2k-ic)b(k)b^\sharp(-k)$}
The effective boundary coefficient is $\widetilde\Gamma=-(2k-ic)b^\sharp(-k)/(a\mathcal D)$. All its ingredients come from initial scattering and the <Robin boundary condition>. Genuine zeros produce pole data; common zeros in numerator and denominator can instead be removable. It is incorrect to assert absence of boundary poles for every real Robin parameter.
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