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

2 votes

nested integrals in functional derivative

I find it helpful in cases such as this to discretize the integrals, so that $g$ becomes a matrix with elements $g_{ij}=g(y_i,x_j)$ and $f$ becomes a vector with elements $f_i=f(x_i)$. Then $J[f]=\sum …
Carlo Beenakker's user avatar
17 votes
Accepted

What variational problem does the parabolic suspension bridge solve?

Quite generally, the shape $y(x)$ of the cable and the shape $w(x)$ of the suspended deck are governed by the Melan equation, a fourth order ODE. A variational formulation is given in Variational form …
Carlo Beenakker's user avatar
4 votes
Accepted

Units of time in the gradient flow equation?

If you wish to interpret the gradient flow equation as an equation of physics (rather than mathematics), then you need to introduce a friction coefficient into your problem, which tells you how rapidl …
Carlo Beenakker's user avatar
12 votes
Accepted

Who first resolved Hilbert's 20th problem?

A discussion of Tonelli's contributions and their relation to Hilbert's work can be found in this AMS bulletin. The original work was published in Italian, Fondamenti di Calcolo delle Variazioni (Bolo …
Carlo Beenakker's user avatar
2 votes

Euler-Lagrange equations and Bellman's principle of optimality

A. multi-dimensional state, one-dimensional time Multi-dimensional extensions $x\in\mathbb{R}^n$ of the one-dimensional Hamilton-Jacobi-Bellman equations have been considered in Consistency of a Simp …
Carlo Beenakker's user avatar
3 votes

Fair surfaces - general mathematical theory

Moreton's thesis work was included in a book that explores fairness measures in modeling from a variety of perspectives: Designing Fair Curves and Surfaces: Shape Quality in Geometric Modeling and Com …
Carlo Beenakker's user avatar
2 votes

Unusual problem of calculus-of-variations. Attempt 2

Since the OP states that $\lambda$ is not fixed from the outset, and assuming that $$J_G\equiv\int_{-1}^1 \cos(\tfrac{1}{2}\pi x)G(x)\,dx\neq 0,$$ we can make $I_G$ arbitrarily large by choosing $f(x …
Carlo Beenakker's user avatar
6 votes
Accepted

The term for problems "like" Brachistocrone?

"Calculus of variations" seems an accepted umbrella term; at least, looking at the corresponding Wikipedia entry, you'll recognize that most problems in this class are of the type you are looking for: …
Carlo Beenakker's user avatar
1 vote
Accepted

Deriving Helfrich's shape equation for closed membranes

The follow-up paper by Helfrich you are searching for is Bending energy of vesicle membranes: General expressions for the first, second, and third variation of the shape energy and applications to s …
Carlo Beenakker's user avatar
7 votes
Accepted

Are all Helmholtz decompositions related?

Q: How are two Helmholtz decompositions related? A: The scalar fields differ by a harmonic function. Starting from a first decomposition $\sigma_1,\Gamma_1$, you can construct a second one by adding t …
Carlo Beenakker's user avatar
0 votes
Accepted

Definition of Euler-Lagrange equation and properties, where can I find?

These lecture notes by Piotr Hajłasz might have the introductory level you are looking for: The lectures will be divided into two almost independent streams. One of them is the theory of Sobolev spac …
Carlo Beenakker's user avatar
12 votes
Accepted

Almgren's mimeographed lectures notes on varifolds

Here is the story behind these notes, and a redirect to On the First Variation of a Varifold, W.K. Allard (1972). a quote from: Selected Works of Frederick J. Almgren
Carlo Beenakker's user avatar
4 votes

Gradient descent relaxation dynamics of a Euler-Lagrange equation

The usual way to ensure the convergence of the steepest descent formulation of the Euler-Lagrange equations, is to introduce a friction term, see The Calculus of Variations by Jeff Calder. Instead of …
Carlo Beenakker's user avatar