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I would like to calculate the uncertainty of the nth Eigenstate of a 1-dim harmonic oscillator. To obtain the result I have to compute the integral

$$\int_{-\infty}^{\infty} \psi^* x^2 \psi \:dx\,,$$ with $$\psi(n,x)=\frac{e^{-\frac{x^2}{2}} H_n(x)}{\pi^{\frac{1}{4}}\sqrt{2^n n!}}\,,$$ where $H_n(x)$ is the Hermite polynomial (degree n) in the physicist version (as implemented in Mathematica). In Mathematica this equals to the Integral over

(2^-n E^-x^2 x^2 HermiteH[n, x]^2)/(Sqrt[π] n!)

Doing this manually gives $1/2+n$, but i can't get Mathematica to solve this integral without specifying $n$. I used `

Assuptions=n ∈ Integers && n >= 0

Is there anyway to compute similar integrals with Mathematica?

Edit: Thanks for you answer, but I should have mentioned, that I'm looking for a way to let Mathematica solve such problems analytical.

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1 Answer 1

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An easy way without struggling with the integral:

FindSequenceFunction[
 Table[Integrate[(2^-n E^-x^2 x^2 HermiteH[n, x]^2)/(Sqrt[π] n!), {x, -Infinity, Infinity}],
       {n, 1, 5}], n]
(*
 1/2 (1 + 2 n)
*)
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  • $\begingroup$ Is there any way to let Mathematica solve this problem analytical? $\endgroup$
    – NicolasW
    Commented Dec 25, 2013 at 23:17
  • $\begingroup$ @Gebbo Not AFAIK $\endgroup$ Commented Dec 26, 2013 at 2:24

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