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Special functions, orthogonal polynomials, harmonic analysis, ordinary differential equations (ODE's), differential relations, calculus of variations, approximations, expansions, asymptotics.
146
votes
Accepted
Why is differentiating mechanics and integration art?
One relevant thing here is that you are referring to differentiating and integrating within the class of so-called elementary functions, which are built recursively from polynomials and complex expone …
56
votes
Accepted
Do these properties characterize differentiation?
Yeah, these force it to be ordinary differentiation. We have to show that for each fixed $x_0 \in \mathbb{R}$, the composite
$$C^\infty(\mathbb{R}) \stackrel{L}{\to} C^\infty(\mathbb{R}) \stackrel{e …
53
votes
Why is differentiating mechanics and integration art?
I hesitate to answer again, but I agree with comments by Deane Yang and others that so far the discussions haven't quite gotten to the bottom of things. (Not that I promise to succeed in doing so now, …
24
votes
Which functions of one variable are derivatives ?
I can't claim much knowledge here, but I am given to understand that the class of differentiable functions (or the class of functions which are derivatives of such) is really quite nasty and complicat …
23
votes
1
answer
2k
views
Monotone functions are differentiable a.e. and Hilbert's Fifth Problem: what's the connection?
In Andrew Gleason's interview for More Mathematical People, there is the following exchange concerning Gleason's work on Hilbert's fifth problem on whether every locally Euclidean topological group is …
13
votes
Accepted
Connectifications?
After seeing wood's last comment (comment #2 under his question), I've decided to add a few words (a bit too many for a comment) which hopefully make clear the force of Qiaochu's answer.
Generally s …
13
votes
Accepted
Functions whose antiderivative behaves like xf(x)
Note: This is a major rewrite of my earlier answer, to include necessary and sufficient conditions applicable to an even wider class of functions.
Instead of expanding to the class of all analytic f …
9
votes
How does the function g(x) behave as x tends to 1?
This appears as Problem 4 of an MSRI Emissary publication, and indeed this problem has been discussed by Noam Elkies. See also his web page (problem 8 here), where he links to a solution.
The conclu …
8
votes
Variable-centric logical foundation of calculus
In one of my comments over at the other thread (this other thread), I had mentioned some discussion at the $n$-Category Café about a differential $\lambda$-calculus (from the looks of it, different to …
7
votes
Accepted
$\sum_{k=1}^n\frac{\sin kx}{k^\alpha} >0\quad\text{for all}\ n=1,2,3,\ldots\ \text{and}\ 0<x...
Comment by Cherng-tiao Perng converted to an answer: It appears that Theorem A of this paper solves your problem.
7
votes
Linear independence of exponential functions: a reference
I will recount the more general statement of linear independence of characters, given in Lang's Algebra book, and credited to Artin. Let $G$ be a group, and $K$ a field. Then distinct homomorphisms $\ …
4
votes
Accepted
Who first found this characterization of Lebesgue integration?
I don't know if this is of help, but I have seen this idea for defining integration elsewhere, specifically on pages 10-11 of Reed and Simon's Functional Analysis. It would go something like this: let …
4
votes
Solvability in differential Galois theory
It's probably not quite what you're looking for, but a necessary and sufficient condition for existence of elementary antiderivatives is given in this nice write-up on Dave Rusin's web, here. He inclu …