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Asymptotic behavior of functions, asymptotic series and related topics

5 votes
Accepted

Asymptotic behavior for the solution of a nonlinear ODE

I believe that a rigorous justification of this asymptotics can be obtained from the papers: J. Malmquist, Acta Math. 73 (1940), 87–129; 74 (1941), 1–64, 109–128; MR0003898 and M. …
Alexandre Eremenko's user avatar
7 votes

textbooks on asymptotic expansions

Asymptotics and special functions. Computer Science and Applied Mathematics. Academic Press, New York-London, 1974. and (an older book) MR0115035 Ford, Walter B. …
6 votes

Growth of (integral of) Laplace transform of a function of compact support as $Re \to -\infty$

It has exponential growth: if your integral is $O(e^{-\sigma\epsilon}), \sigma\to -\infty,$ then the support of your function $f$ is contained in $[0,\epsilon]$. This follows from the inversion formul …
Alexandre Eremenko's user avatar
3 votes
Accepted

Asymptotic behavior of a solution of an ODE

It is possible to solve it explicitly in terms of the Airy function. Airy's equation in the standard form is $$y''=xy.$$ Your equation is reduced to this by $x\mapsto-x$ followed by a shift of the ind …
Alexandre Eremenko's user avatar
4 votes
Accepted

Asymptotic Behaviour of Solutions to a Riccati-type ODE with Small Forcing Term

In your example you obtained two linearly independent solutions with different behavior: $\cot(1/r)\sim r,\; r\to\infty$, so your second solution is $O(r^{-2})$. This is the general pattern if you as …
Alexandre Eremenko's user avatar
2 votes

Reference request: using integral equations to study asymptotics of ODEs

Fedoryuk, Mikhail V. Asymptotic analysis. Linear ordinary differential equations. Springer-Verlag, Berlin, 1993. viii+363 pp. ISBN: 3-540-54810-6 Wasow, Wolfgang Asymptotic expansions for ordinary d …
Alexandre Eremenko's user avatar
9 votes
Accepted

Riemann surface from Riccati equation

The answer to the highlighted question is "no". When $V$ is a polynomial, the general solution of the Riccati equation is single valued, it is a meromorphic function in the complex plane. To prove the …
Alexandre Eremenko's user avatar
3 votes

Asymptotic behaviour/upper bound for $\int_0^{\infty} \exp(-c x^a+K x^b)dx$ for $a>b>0$ as $...

This is a simple example for the Laplace Method of asymptotic evaluation of integrals. The essence of the method is that the main contribution to the integral comes from a small neighborhood of the cr …
Alexandre Eremenko's user avatar
0 votes

Quantitative Weierstrass Approximation and Paley-Wiener for the Laplace Transform

The answer to your question is "no" in a very strong sense: I will construct $a$ such that $a(x,0)\neq 0$ and $$\int_0^1e^{\lambda x}a(x,1/\lambda)dx\equiv 0.$$ Begin with $a(x)$ infinitely smooth, no …
Alexandre Eremenko's user avatar
2 votes
Accepted

Limit (at infinity) for the lowest eigenvalue of a perturbed harmonic oscillator

Consider two operators $L_1w=-w''+U(x)w$ with eigenvalues $\lambda_k$ and $L_2w=-w''+V(x)w$ with eigenvalues $\mu_k$. If $U\geq V$ then $\lambda_k\geq \mu_k$. To prove this consider the Rayleigh ratio …
Alexandre Eremenko's user avatar
3 votes
Accepted

Largest asymptotic growth for $2f(x)-f(2x)$

Let us discretise the problem by setting $a_n=2^{-n}f(2^n)$, $b_n=2^{-n-1}\Delta_f(2^n)$. Then your relation becomes, $$b_n=a_n-a_{n+1}.$$ since $a_n,b_n$ are non-negative, we conclude that $$\sum_{n= …
Alexandre Eremenko's user avatar
1 vote

Asymptotic behavior of the solution of the high degree differential equation $(x^{2n}y^{(n)}...

Anyway, there is an algorithm of obtaining these asymptotics. …
Alexandre Eremenko's user avatar
2 votes

Proof of Szegö asymptotic theorem

Asymptotics for the zeros of the partial sums of ez. I. Rocky Mountain J. Math. 21 (1991), no. 1, 99–121. MR1071774 Varga, R. S.; Carpenter, A. J. … Asymptotics for the zeros of the partial sums of ez. II. Computational methods and function theory (Valparaíso, 1989), 201–207, Lecture Notes in Math., 1435, Springer, Berlin, 1990. T. …
Alexandre Eremenko's user avatar