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COMPLETE MONOTONICITY OF A FUNCTION INVOLVING THE TRI- AND TETRA-GAMMA FUNCTIONS

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Abstract. The psi function ψ(x) is defined by ψ(x) = Γ'(x) / Γ(x) and ψ(i)(x) for i ∈ N denote polygamma functions, where Γ(x) is the gamma function. In the paper, the author proves that the function [ψ'(x)]2 + ψ''(x) - x2 + λx + 12 / 12x4(x + 1)2 is completely monotonic on (0,∞) if and only if λ ≥ 0, and so is its negative if and only if λ ≥ 4. From this, some inequalities are re ned and sharpened.

Abstract

Abstract. The psi function ψ(x) is defined by ψ(x) = Γ'(x) / Γ(x) and ψ(i)(x) for i ∈ N denote polygamma functions, where Γ(x) is the gamma function. In the paper, the author proves that the function [ψ'(x)]2 + ψ''(x) - x2 + λx + 12 / 12x4(x + 1)2 is completely monotonic on (0,∞) if and only if λ ≥ 0, and so is its negative if and only if λ ≥ 4. From this, some inequalities are re ned and sharpened.

참고문헌 (23)

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  3. Bai-Ni Guo, "A CLASS OF COMPLETELY MONOTONIC FUNCTIONS INVOLVING DIVIDED DIFFERENCES OF THE PSI AND TRI-GAMMA FUNCTIONS AND SOME APPLICATIONS", 대한수학회지, 48(3), pp.655~667 (2011), 대한수학회
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