Strong coefficientwise Hankel-total positivity conjecture for the GKP recurrence

Let T(n,k)T(n,k) be defined by the shifted GKP recurrence

T(n,k)=[α~(n1)+β~k+γ~]T(n1,k)+[α~(n1)+β~(k1)+γ~]T(n1,k1),T(n,k)=[\widetilde{\alpha}(n-1)+\widetilde{\beta}k+\widetilde{\gamma}]T(n-1,k)+[\widetilde{\alpha}'(n-1)+\widetilde{\beta}'(k-1)+\widetilde{\gamma}']T(n-1,k-1),

and let Pn(x;μ~)P_n(x;\widetilde{\bm{\mu}}) be its row-generating polynomials, where μ~=(α~,β~,γ~,α~,β~,γ~)\widetilde{\bm{\mu}}=(\widetilde{\alpha},\widetilde{\beta},\widetilde{\gamma},\widetilde{\alpha}',\widetilde{\beta}',\widetilde{\gamma}'). A sequence is coefficientwise Hankel-totally positive when every minor of its Hankel matrix has nonnegative coefficients in the indicated indeterminates.

Strong coefficientwise Hankel-total positivity conjecture for the GKP recurrence. The sequence

P=(Pn(x;μ~))n0\bm{P}=(P_n(x;\widetilde{\bm{\mu}}))_{n\geq 0}

of row-generating polynomials of this shifted recurrence is coefficientwise Hankel-totally positive, jointly in the seven indeterminates x,α~,β~,γ~,α~,β~,γ~x,\widetilde{\alpha},\widetilde{\beta},\widetilde{\gamma},\widetilde{\alpha}',\widetilde{\beta}',\widetilde{\gamma}'.

This is presented as a stronger version of the unshifted GKP positivity conjecture, obtained by an affine reparametrization, and remains unproved in the supplied text.

Sources & referencesView supporting material

Primary source

Jesús Salas and Alan D. Sokal, “The Graham–Knuth–Patashnik recurrence: Symmetries and continued fractions”, arXiv:2008.03070 (2021).

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