3
votes
1answer
89 views

Asymptotic behavior of a sequence of integrals

I am interested in the asymptotic behavior of sequences $(I_n)$ and $(J_n)$ as $n \rightarrow \infty$, where $$I_n = \int_{1}^{\infty}\frac{e^{-nx^2}}{x^2}\, dx,$$ and $$J_n = ...
0
votes
0answers
43 views

How I can evalute numerically this improper complex integral?

I need a hand with the numerical evaluation, in Mathematica, for this integral: $$f(t)=\int_{-\infty}^\infty Exp\{it(\omega_H-\omega_l-\omega_k) - \sum _{j\neq(l,k)} S_j [1-e^{-it\omega_j}]\}\, dt$$ ...
2
votes
1answer
49 views

Gaussian integral asymptotics

I am trying to derive the asymptotics of $$\int_{2\sqrt{m}}^{\infty}e^{-\frac{x^2}{4}}x^mdx$$ as $m\to\infty$ with no success. I tried integrating by parts, but could get no nice expression. Any help ...
1
vote
0answers
19 views

parametric integral and asymptotic representation

Here is a parametrial integral $$I(a)=\int_0^{\pi}\int_0^{\pi} ...
3
votes
1answer
60 views

Approximating an integral with elementary functions

Consider the integral $$\int_1^\infty\frac{\exp(-nx)}{x}dx$$ We get:$$\int_1^\infty\frac{\exp(-nx)}{x}dx=n\int_ n^\infty\frac{\exp(-x)}{x}=nE_1(n)$$ My question is, can we approximate this integral ...
2
votes
2answers
51 views

Prove the following: Product of Roots

$1^{(1/1)} \cdot 2^{(1/2)} \cdot 3^{(1/3)} \cdot 4^{(1/4)} \cdot 5^{(1/5)} $.... diverges well I don't really know if it does but my gut tells me it does: I can take the log of this product to ...
1
vote
0answers
96 views

Asymptotics of an integral

Consider an integral $$ I(x) = \int\limits_{\mathbb{R}^n} e^{i\xi x } \delta(\xi^2-k^2)\chi( (\xi-k,\gamma)) \, d\xi $$ where $x, k, \gamma \in \mathbb{R}^n$, $|\gamma| = 1$ and $(x,y)\equiv xy = ...
2
votes
1answer
115 views

Asymptotics of an improper integral

I have to show that if $x \to \infty$, then $$ \int\limits_{\mathbb{R}^d} \frac{e^{i\xi x}}{\xi^2 + 2k\xi}d\xi = O\left(|x|^{-\frac{d-1}{2}} \right) \;\;\; \; d\geqslant2, \;\;\; k\in \mathbb{C}^d ...