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Special functions, orthogonal polynomials, harmonic analysis, ordinary differential equations (ODE's), differential relations, calculus of variations, approximations, expansions, asymptotics.

4 votes

Weighted Hardy Inequality for bounded domains

Sorry, I can't access the image on my browser; it won't load for some reason. Could you please type out the inequality in Latex? So I'll just have to guess what you might want; apologies if this is n …
Zen Harper's user avatar
  • 1,990
5 votes

Splines, harmonic analysis, singular integrals.

If you want to extend differentiation to all continuous functions, then (provided you have some convenient mathematical properties of the extension) you are FORCED to use distributions or roughly equi …
Zen Harper's user avatar
  • 1,990
1 vote

On linear independence of exponentials

Still thinking about the interesting question! Not an answer, but too big for a comment. To show what I meant in my comment to Daniel Litt's answer about the difference between uniform absolute conv …
Zen Harper's user avatar
  • 1,990
2 votes

The maximum of a real trigonometric polynomial

Even in the special case where $f(x) \geq 0$ for all $x$, there can't be any simple answer involving the coefficients $(a_n)$, $(b_n)$. You're basically asking to estimate the $L^\infty$ norm of a tri …
Zen Harper's user avatar
  • 1,990
18 votes
1 answer
3k views

Let a function f have all moments zero. What conditions force f to be identically zero?

Throughout, let $f$ be a Lebesgue measurable function (or continuous if you wish, but this is probably no easier). (Questions with distributions etc. are possible also but I want to keep things simple …
Zen Harper's user avatar
  • 1,990
10 votes

When I can safely assume that a function is a Laplace transform of other function?

This kind of question is very interesting, and I too would like to know answers. Sorry to self-publicise; I hope it's not regarded as impolite, but since I have also considered this exact kind of ques …
Zen Harper's user avatar
  • 1,990