Schur-convex function

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In mathematics, a Schur-convex function, also known as S-convex, isotonic function and order-preserving function is a function $f: \mathbb{R}^d\rightarrow \mathbb{R}$ , for which if $\forall x,y\in \mathbb{R}^d$ where $x$ is majorized by $y$ , then $f(x)\le f(y)$ . Named after Issai Schur, Schur-convex functions are used in the study of majorization.