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A surface is a generalization of a plane which needs not be flat, that is, the curvature is not necessarily zero. This is analogous to a curve generalizing a straight line

24 votes
Accepted

What is the analog of the "Fundamental Theorem of Space Curves," for surfaces, and beyond?

I've added a few sentences to my answer to clarify something that some readers may be wondering about, which is why there isn't as simple an answer for surfaces in $3$-space as there is for curves in …
Robert Bryant's user avatar
19 votes

A necessary and sufficient condition for a space curve to lie on a ellipsoid

There is a straightforward way to deduce necessary conditions for a space curve to lie on an ellipsoid, and it's really a matter of calculation to make these conditions explicit in terms of the curvat …
Robert Bryant's user avatar
18 votes
Accepted

How useful/pervasive are differential forms in surface theory?

Well, there's really not a whole lot more to say beyond what Deane already wrote. He certainly hit the main points, but maybe I can expand a bit on what he wrote and comment on my own experience over …
Robert Bryant's user avatar
18 votes
Accepted

When does the shape operator commute with a derivative?

The question is essentially equivalent to the following classical question: Given a smooth surface $S$ and a bundle map $L:TS\to TS$, when does there exist an immersion $x:S\to \mathbb{R}^3$ such tha …
Robert Bryant's user avatar
17 votes
Accepted

Geodesics on the twisted pseudosphere (Dini's surface)

To answer Joseph's questions: First, it's not impossible to integrate the geodesic flow of the hyperbolic plane in these coordinates, but the formulae I got aren't very nice, so I'm not going to type …
Robert Bryant's user avatar
17 votes
Accepted

Variation of curvature with respect to immersion?

If you just calculate using the moving frame, you'll get the answer for the variation of the principal curvatures in a few lines: $$ \delta\kappa_i = \mathrm{Hess}(u)(e_i,e_i) + \kappa_i^2\,u . $$ Her …
Robert Bryant's user avatar
16 votes
Accepted

Are there some intrinsic invariants of surfaces other than Gaussian curvature?

As others have pointed out, it's not hard to show that any function $F(\kappa_1,\kappa_2)$ that is intrinsic to the surface metric must be a function of $K = \kappa_1\kappa_2$, so that settles what on …
Robert Bryant's user avatar
14 votes
Accepted

A variant of the Monge-Cayley-Salmon theorem?

Setting aside the assumption that $\phi$ be a polynomial mapping for the moment (however, see below for a construction of a large family of polynomial solutions), if one makes the 'nondegeneracy' assu …
Robert Bryant's user avatar
12 votes

Geometric meaning of derivatives of the curvature

This is not really an answer, but it's too long for a comment, so I'm posting it this way. One way in which the expression you are considering has appeared in recent years is via the heat equation sh …
Robert Bryant's user avatar
8 votes
Accepted

homogeneous surface in $\mathbb{R}^4$

I'm rearranging my answer a little bit because I realized that I overlooked an apparent possibility (that turns out not to occur), and I didn't want my answer to be misleading: If the surface in Eucl …
Robert Bryant's user avatar
7 votes
Accepted

Construction of a linear Weingarten surface from a space curve

You'll find a discussion of the analysis of linear Weingarten surfaces via exterior differential systems in these lecture notes of mine. Particularly look at Section 5.1, where it is discussed at len …
Robert Bryant's user avatar
7 votes

If a triangle can be displaced without distortion, must the surface have constant curvature?

This is sort of an answer and sort of not. I'll let you be the judge: Suppose you formulate the question, not in terms of 'motion' (which you left vague) but terms of 'freely copying' a triangle $T$ …
Robert Bryant's user avatar
6 votes

Minimal surface as varities

I assume that you are asking for a proof of the Weierstrass-Enneper representation theorem that, roughly speaking, tells you how to express solutions of the minimal surface equation in terms of holomo …
Robert Bryant's user avatar
6 votes
Accepted

Can every smooth space curve be realized as an origami curved crease?

Note: I'm revising my answer to make the argument/construction more transparent. In the previous version, I stated an existence result about flat surfaces, but didn't indicate a proof (because, at th …
Robert Bryant's user avatar
5 votes
Accepted

The class of uniformly accelerated curves and surfaces

I don't know what you might mean by 'uniformly accelerated surface', but I think that, by 'uniformly accelerated curve', you mean a curve in the plane parametrized in such a way that its velocity at t …
Robert Bryant's user avatar

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