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In mathematics, majorization is a preorder on vectors of real numbers. For a vector , we denote by the vector with the same components, but sorted in descending order. Given , we say that weakly majorizes (or dominates) from below written as iff : where and are the elements of and , respectively, sorted in decreasing order. Equivalently, we say that is weakly majorized (or dominated) by from below, denoted as . Similarly, we say that weakly majorizes from above written as iff : Equivalently, we say that is weakly majorized by from above, denoted as . If and in addition we say that majorizes (or dominates) written as . Equivalently, we say that is majorized (or dominated) by , denoted as . It is easy to see that if and only if and . Note that the majorization order do not depend on the order of the components of the vectors or . Majorization is not a partial order, since and do not imply , it only implies that the components of each vector are equal, but not necessarily in the same order. Regrettably, to confuse the matter, some literature sources use the reverse notation, e.g., is replaced with , most notably, in Horn and Johnson, Matrix analysis (Cambridge Univ. Press, 1985), Definition 4.3.24, while the same authors switch to the traditional notation, introduced here, later in their ''Topics in Matrix Analysis'' (1994). A function is said to be Schur convex when implies . Similarly, is Schur concave when implies The majorization partial order on finite sets, described here, can be generalized to the Lorenz ordering, a partial order on distribution functions. ==Examples== The order of the entries does not affect the majorization, e.g., the statement is simply equivalent to . (Strong) majorization: . For vectors with ''n'' components : (Weak) majorization: . For vectors with ''n'' components: : 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「majorization」の詳細全文を読む スポンサード リンク
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