View source for Convexity, logarithmic

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The property of a non-negative function $f$, defined on some interval, that can be described as follows: If for any $x_1$ and $x_2$ in this interval and for any $p_1 \ge 0$, $p_2 \ge 0$ with $p_1+p_2=1$ the inequality
$$
f(p_1x_1 + p_2x_2) \le f(x_1)^{p_1} \cdot f(x_2)^{p_2}
$$
is satisfied, $f$ is called logarithmically convex. If a function is logarithmically convex, it is either identically equal to zero or is strictly positive and $\log f$ is a [[convex function (of a real variable)]].