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Questions on the calculus of variations, which deals with the optimization of functionals mostly defined on infinite dimensional spaces.

5 votes

Area of the minimal surface of a non-planar quadrilateral in 3d

This paper seems to give a partial answer to the posed question, for skew quadrilaterals that project to rectangles: Furui, Sadataka, and Bilal Masud. "Numerical calculation of a minimal surface u …
Joseph O'Rourke's user avatar
25 votes
Accepted

How can you compute the maximum volume of an envelope(used to enclose a letter)?

Your question is a variant of the teabag problem. I don't believe an exact answer is known, but for the $1 \times 1$ square teabag, the maximum volume is about $0.2$:                     (Image …
Joseph O'Rourke's user avatar
7 votes

Largest possible volume of the convex hull of a curve of unit length

Here is an image of the optimal open convex curve. Taken from Open Problems from CCCG 2012, based on this paper, which cites Nudel'man (1975): Paolo Tilli. "Isoperimetric inequalities for conve …
Joseph O'Rourke's user avatar
4 votes

Smallest area shape that covers all unit length curve

P.A.P. Moran proved in 1946, in "On a Problem of S. Ulam" [J. London Math. Soc. 1946 s1-21: 175-179] this theorem: If $C$ is a curve of unit length in the plane, and $|K$| is the area of its small …
Joseph O'Rourke's user avatar
6 votes

Closed curve whose neighborhood is as large as possible

Just to emphasize Thomas Richard's remark about smoothness, unless I've miscalculated, a $\frac{1}{4} L$-square leads to area $$2 \epsilon L - \epsilon^2 (4-\pi) < 2 \epsilon L \;.$$        Added …
Joseph O'Rourke's user avatar
3 votes
Accepted

Names of certain surfaces

If Surface I yet has no name, I would christen it Winged Victory. :-)           
Joseph O'Rourke's user avatar