The inclusive sets Z n are zonotopes of high order. Zonotopes are special polytopes. For order 1, the zonotopes are always boxes. A box is a rectangle aligned with the coordinate axes. For order 2, the zonotope is the Minkowski sum of a box and a parallelepiped, for oder 3 the Minkowski sum of a box and two parallelepipeds, and so on.
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The visible view of the plane defined by the minimal and maximal x and y values. This is the performance parameter of the algorithm. The quality of the enclosures increases with the order. An order of 1 always produces interval enclosures and therefore performs very poorly. An order of 5 is usually appropriate.