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arXiv · 2105.05583

Total positivity of some polynomial matrices that enumerate labeled trees and forests, I. Forests of rooted labeled trees

Alan D. Sokal
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Abstract

We consider the lower-triangular matrix of generating polynomials that enumerate $k$-component forests of rooted trees on the vertex set $[n]$ according to the number of improper edges (generalizations of the Ramanujan polynomials). We show that this matrix is coefficientwise totally positive and that the sequence of its row-generating polynomials is coefficientwise Hankel-totally positive. More generally, we define the generic rooted-forest polynomials by introducing also a weight $m! \, \phi_m$ for each vertex with $m$ proper children. We show that if the weight sequence $\phi$ is Toeplitz-totally positive, then the two foregoing total-positivity results continue to hold. Our proofs use production matrices and exponential Riordan arrays.

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Alan D. Sokal. 2021-05-12. Total positivity of some polynomial matrices that enumerate labeled trees and forests, I. Forests of rooted labeled trees. https://doi.org/10.1007/s00605-022-01687-0

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