Conjectured convolution inverse for the Tutte q-polynomial transform

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Let RR be the rectangular poset formed by the product of the chains 0,…,ρ0,\dots,\rho and 0,…,ν0,\dots,\nu. For intervals [a,b][a,b] and [c,d][c,d] in RR, let α\alpha be the convolution kernel determined by

α(a,b;c,d)=(ac)q(bd)qq(a−c)(b−d).\alpha(a,b;c,d)={\binom{a}{c}}_{q}{\binom{b}{d}}_{q}q^{(a-c)(b-d)}.

The convolution inverse β\beta is defined by α∘β=β∘α=δ\alpha\circ\beta=\beta\circ\alpha=\delta, where the identity kernel is δacδbd\delta_a^c\delta_b^d.

Conjectured convolution-inverse formula. For the relevant indices a,b,c,da,b,c,d,

β(a,b;c,d)=(−1)(a−c)+(b−d)(ac)q(bd)qq(∣(a−c)−(b−d)∣2)(1+q∣(a−c)−(b−d)∣−qmax⁡(a−c,b−d)).\beta(a,b;c,d)=(-1)^{(a-c)+(b-d)}{\binom{a}{c}}_{q}{\binom{b}{d}}_{q}q^{\binom{|(a-c)-(b-d)|}{2}}\left(1+q^{|(a-c)-(b-d)|}-q^{\max(a-c,b-d)}\right).

This formula would invert the rank-generating-function transform relating the Tutte qq-polynomial to the rank generating function of a qq-matroid. It was obtained from computational experimentation and is presented as a conjecture; no proof or resolution is supplied in the source.

References

Primary source

Guus Bollen, Henry Crapo and Relinde Jurrius, “The Tutte q-Polynomial”, arXiv:1707.03459 (2017).

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