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

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
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
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
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
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