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Acta Mathematica Vietnamica

A New Type of Operator Convexity

Trung-Hoa Dinh , Thanh-Duc Dinh , icon-email Bich-Khue T. Vo

Abstract

Let r,s be positive numbers. We define a new class of operator (r,s)-convex functions by the following inequality f([λAr+(1λ)Br]1/r)[λf(A)s+(1λ)f(B)s]1/s, where A,B are positive definite matrices and for any λ[0,1]. We prove the Jensen, Hansen-Pedersen, and Rado type inequalities for such functions. Some equivalent conditions for a function f to become operator (r,s)-convex are established.