Anderson–Vamanamurthy–Vuorinen elliptic-integral monotonicity conjecture

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Let K(r)=(π/2)F(1/2,1/2;1;r2)\mathcal{K}(r)=(\pi/2)F(1/2,1/2;1;r^2) be the complete elliptic integral of the first kind. For r∈(0,1)r\in(0,1), set r′=1−r2r'=\sqrt{1-r^2}. Anderson–Vamanamurthy–Vuorinen's conjecture. The function

r↦K(r)/ln⁡(4/r′)−1(r′)2r\mapsto\frac{\mathcal{K}(r)/\ln(4/r')-1}{(r')^2}

is increasing from (0,1)(0,1) onto (π/ln⁡16−1,1/4)(\pi/\ln 16-1,1/4). This is a special elliptic-integral instance of the broader open-problem context surrounding Ramanujan's asymptotic formula for the zero-balanced hypergeometric function; the supplied text does not establish whether this particular conjecture has been resolved.

References

Primary source

Miao-kun Wang, Zhen-hang Yang and Tie-hong Zhao, “An affirmative answer to an open problem on Ramanujan's asymptotic formula of zero-balanced hypergeometric function”, arXiv:2504.04521 (2025).

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