Logarithmically convex function

A function \( f: (a, b) \to \mathbb{R} \) is said to be logarithmically convex on the interval \( (a, b) \) if for any \( x, y \in (a, b) \) and \( \lambda \in [0, 1] \), the following inequality holds: \[ f(\lambda x + (1 - \lambda) y) \leq (f(x)^{\lambda}