Alzer–Qiu's monotonicity and convexity conjecture for the elliptic-integral ratio

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Let K(r)\mathscr{K}(r) denote the complete elliptic integral of the first kind for r∈(0,1)r\in(0,1), and define

G(r)=log⁡(2K(r)/π)log⁡((arth⁡r)/r).G(r)=\frac{\log(2\mathscr{K}(r)/\pi)}{\log((\operatorname{arth} r)/r)}.

Alzer–Qiu's conjecture. The function GG is strictly increasing and convex from (0,1)(0,1) onto (3/4,1)(3/4,1).

This conjecture refines the best possible exponents in bounds approximating the complete elliptic integral by (arth⁡r)/r(\operatorname{arth} r)/r. The source notes that the conjecture remained difficult to prove; no resolution is supplied here.

References

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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