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We say a rectangle has orientation $\theta$ if the vector from its center to the middle of its shortest side (parallel to the longest side) has some angle $\theta$ with X axis.

Consider a planar convex region $C$ fixed in $\mathbb{R}^2$. Let us draw $R_{1}$, the smallest rectangle containing $C$ and call the orientation of $R_{1}$, $\theta_1$. Let us also draw the rectangle $R_{2}$, the largest rectangle contained within $C$ and let its orientation be $\theta_2$.

Example illustration

Question: Which planar convex region $R$ maximizes $|\theta_1-\theta_2|$ ?

Note 1: If either rectangle is a square, the $\theta$ values won't be unique and we take the smallest value of $|\theta_1-\theta_2|$ as the orientation difference.

Note 2: The same question can be asked with area replaced with perimeter.

Related: bounds on largest internal rectangle area and considering a simple case: right triangles

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    $\begingroup$ I'm really struggling to parse the question. "the orientation of a rectangle to be along its length" - what is this supposed to mean? $\endgroup$
    – Wojowu
    Commented Jul 13, 2023 at 19:27
  • $\begingroup$ With serious inputs from Vallev (thanks!), the question has been edited. Hope it is clearer now. Thanks. $\endgroup$ Commented Jul 15, 2023 at 2:21

1 Answer 1

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Consider the convex hull of the union of a unit circle centered at the origin and an axis-aligned rectangle centered at the origin with dimensions of $2\times \sqrt{2}$. Now trim this shape slightly by cutting away the left and right edges by a width of $\epsilon$. This shape has a horizontal maximal inscribed rectangle and a vertical minimal containing rectangle.

unrivaled artistic skill

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  • $\begingroup$ Thanks for this very simple and nice construction. It appears to solve both area and perimeter cases of the question. $\endgroup$ Commented Jul 17, 2023 at 1:44

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