Skip to main content

All Questions

Filter by
Sorted by
Tagged with
7 votes
1 answer
337 views

If $f(x) = \sum_{n=0}^\infty a_n x^n$, then $\int_{-\infty}^\infty f(x^2) dx = \pi i a_{-\frac{1}{2}}$

I've noticed a curious relationship between the coefficient $a_n$ for a power series and the integral of the real line. For instance, take $f(x) = e^{-x} = \sum_{n=0}^\infty \frac{(-1)^n}{n!} x^n$. ...
Caleb Briggs's user avatar
  • 1,730
4 votes
1 answer
249 views

Does the analytical continuation of $\sum f(n) x^n $ always have a branch cut if $f(z)$ has a pole?

I suspect the answer to the title question is 'no', but I'm hoping to find an explicit counterexample. Also, I am requiring that $\sum f(n) x^n $ has a finite radius of convergence, otherwise, the ...
Caleb Briggs's user avatar
  • 1,730
2 votes
2 answers
248 views

Assigning values to divergent oscillating integrals

I have recently run into a number of divergent oscillating integrals in various contexts. Thus, I have been led to desire general methods for assigning values to divergent oscillating integrals. All ...
Caleb Briggs's user avatar
  • 1,730
4 votes
1 answer
2k views

Exchanging series and integrals

I know that I can use Lebesgue or monotone convergence theorem to exchange limit of partial sums and a Lebesgue integral, given a power series or a generic function series. But in general given a ...
Coltrane8's user avatar
1 vote
1 answer
415 views

What are the consequences if we could express tangent via logarithm in an algebraic system? [closed]

Working on an algebra of divergent integrals I came to the following relation: If $\tau=\int_0^\infty dx$ then $$\ln (\tau+a)=\int_{0}^\infty \psi'(x+1/2+a)dx$$ and this directly gives the following ...
Anixx's user avatar
  • 10.1k