Schur-convex function if and only if formula_6 for all formula_7 holds for all 1≤"i"≠"j"≤"d". Schur-convex function In mathematics, a Schur-convex function, also known as S-convex, isotonic function and order-preserving function is a function formula_1 that for all formula_2 such that formula_3 is majorized by formula_4, one has that formula_5. Named after Issai Schur, Schur-convex functions are used in the study of majorization. Every function that is convex and symmetric is also Schur-convex. The opposite implication is not true, but all Schur-convex functions are symmetric (under permutations of the arguments). A function "f" is 'Schur-concave' if its negative, -"f", is Schur-convex. If "f"
Parallel projection Parallel projection A parallel projection is a projection of an object in three-dimensional space onto a fixed plane, known as the "projection plane" or "image plane", where the "rays", known as "lines of sight" or "projection lines", are parallel to each other. It is a basic tool in descriptive geometry. The projection is called "orthographic" if the rays are perpendicular (orthogonal) to the image plane, and "oblique" or "skew" if they are not. A parallel projection is a particular case of "projection" in mathematics and "graphical projection" in technical drawing. Parallel projections can be seen as the limit of a