A harmonic mean inequality for the q-gamma function

In 1984, Kairies proved that for all positive real numbers x the geometric mean of $$\Gamma _q(x)$$ and $$\Gamma _q(1/x)$$ is greater than or equal to 1, that is, $$\begin{aligned} 1\le \sqrt{\Gamma _q(x)\Gamma _q(1/x)} \quad (0<q\ne 1), \end{aligned}$$ where $$\Gamma _q$$ denotes the q-gamma function. This result can be improved if $$q\in (0,1)$$ . We show that for all $$x>0$$ the harmonic mean of $$\Gamma _q(x)$$ and $$\Gamma _q(1/x)$$ is greater than or equal to 1, that is, $$\begin{aligned} 1\le \frac{2}{1/\Gamma _q(x)+1/\Gamma _q(1/x)} \quad (0<q<1) \end{aligned}$$ with equality if and only if $$x=1$$ .

[1]  On an Iteration Leading to a q-Analogue of the Digamma Function , 2011, 1111.0250.

[2]  Theq-gamma function forx<0 , 1980 .

[3]  A. Salem A certain class of approximations for the $q$-digamma function , 2016 .

[4]  Ahmed Salem,et al.  A completely monotonic function involving q-gamma and q-digamma functions , 2012, J. Approx. Theory.

[5]  A. Salem Sharp lower and upper bounds for the q-gamma function , 2020 .

[6]  A. Salem Some classes of completely monotonic functions related to q-gamma and q-digamma functions , 2016 .

[7]  F. Alzahrani,et al.  Sharp bounds for a ratio of the q-gamma function in terms of the q-digamma function , 2021 .

[8]  F. Alzahrani,et al.  Improvements of bounds for the q-gamma and the $q$-polygamma functions , 2017 .

[9]  H. Alzer On Gautschi's harmonic mean inequality for the gamma function , 2003 .

[10]  Martin E. Muldoon,et al.  Inequalities and monotonicity properties for gamma and q -gamma functions , 1994, 1301.1749.

[11]  Charakterisierungen und Ungleichungen für die q-Factorial-Funktionen , 1984 .

[12]  A. Salem Monotonic functions related to the q-gamma function , 2016 .

[13]  A. Salem An infinite class of completely monotonic functions involving the q-gamma function , 2013 .

[14]  W. Gautschi A Harmonic Mean Inequality for the Gamma Function , 1974 .

[15]  H. Alzer Inequalities for the gamma function , 1999 .

[16]  R. Stanley What Is Enumerative Combinatorics , 1986 .

[17]  Theq-gamma function forx<0 , 1980 .

[18]  Sharp bounds for the q-gamma function in terms of the Lambert W function , 2019 .

[19]  Special Functions: The Gamma and Beta Functions , 1978 .

[20]  Richard Askey,et al.  The q-Gamma and q-Beta Functions† , 2007 .

[21]  H. Alzer ON A GAMMA FUNCTION INEQUALITY OF GAUTSCHI , 2002, Proceedings of the Edinburgh Mathematical Society.

[22]  Horst Alzer,et al.  Inequalities involving Γ( x ) and Γ(1/ x ) , 2006 .

[23]  Horst Alzer A harmonic mean inequality for the gamma function , 1997 .