Conjectures on convexity and absolute monotonicity of auxiliary elliptic-integral functions

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Let ff, GG, h11h_{11} and h12h_{12} be the functions introduced in the source, let f7f_7 be the function from Lemma 1(7), and define

h13(r)=r2log(2K(r)π),r(0,1).h_{13}(r)=r^{-2}\log\left(\frac{2\mathscr{K}(r)}{\pi}\right),\qquad r\in(0,1).

Auxiliary-function conjectures. (1) The function ff is convex on (0,1)(0,1). (2) The functions h11h_{11} and h12h_{12} are both strictly increasing and convex on (0,1)(0,1), with ranges (79/960,log(π/2))(79/960,\log(\pi/2)) and (517/604800,)(517/604800,\infty), respectively. (3) The coefficients of the Maclaurin series expansions of ff, GG, f7f_7, h11h_{11}, h12h_{12} and h13h_{13} are all positive; in particular, these functions are all absolutely monotone on (0,1)(0,1).

These claims arise from computed series expansions and are intended to provide stronger regularity and positivity properties for the functions used in the elliptic-integral inequalities. The supplied text gives no proof or resolution.

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Primary source

Song-Liang Qiu, Qi Bao, Xiao-Yan Ma and Hong-Biao Jiang, “On a Conjecture Concerning the Approximates of Complete Elliptic Integral of the First Kind by Inverse Hyperbolic Tangent”, arXiv:2103.04072 (2021).

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