# Homework Help: Hermite polynomials and Schwartz space

1. Jan 20, 2012

### Anden

1. The problem statement, all variables and given/known data
I'm supposed to show that the Hermite Polynomials are in Schwartz space

$h_n = \frac{1}{\sqrt{n!}}(A^{\dagger})^n h_0$

where

$A^{\dagger} = \frac{1}{\sqrt{2}}(-\frac{d}{dx} + x)$

and

$h_0 = \pi^{-1/4}e^{-x^2/2}$

2. Relevant equations
Seminorm: $\|\phi\|_{\alpha,\beta} = \sup_{x\in\mathbb{R}^n}|x^{\alpha}\partial^{\beta}\phi(x)|$

($\alpha$ and $\beta$ are multi-indices)

Schwartz space is defined as being the set
$S(\mathbb{R}^n) = \{\phi\in C^{\infty}(\mathbb{R}^n)|\|\phi\|_{\alpha,\beta}< \infty \ \forall\alpha,\beta\in\mathbb{N}^n\}$

3. The attempt at a solution
My idea was to show that $A^{\dagger}: S(\mathbb{R})\rightarrow S(\mathbb{R})$ is a linear map from Schwartz space to itself. Then it would be enough to show that $h_0$ is in Schwartz space for the problem to be solved

Multiplication with $x$ and $d/dx$ are linear maps from Schwartz space to itself since according to the definition of the seminorm $\|\cdot\|_{\alpha,\beta},\ \alpha,\beta\in\mathbb{Z}_{>0}$ $\|x\phi(x)\|\leq \|\phi(x)\|_{\alpha+1,\beta} + \beta\|\phi(x)\|_{\alpha,\beta-1}$ and $\|\frac{d}{dx}\phi(x)\| = \|\phi(x)\|_{\alpha,\beta+1}$.
This means that the first part is finished.

Is this approach valid or have I completely misunderstood the concept? Also, how do I show that $e^{-x^2/2}\in S(\mathbb{R})$?