Friday, 22 December 2006

ca.analysis and odes - Asymptotics of Hermite and hypergeometric function

I am looking for the asymptotics of the following integral




intmathbbRH2m(x)rme2alpha2x2rmdx=2m1/2alpha2m1(12alpha2)mGamma(m+1/2) 2F1left(m,m,1/2m,fracalpha22alpha21right)intmathbbRH2m(x)rme2alpha2x2rmdx=2m1/2alpha2m1(12alpha2)mGamma(m+1/2) 2F1left(m,m,1/2m,fracalpha22alpha21right)




where HmHm is the mrmthmrmth Hermite polynomial (orthogonal under the weight rmex2rmex2), and 2F12F1 is the hypergeometric function.



I found this formula from p. 803 of "Table of Integrals, Series, and Products" by Gradshteyn-Ryzhik. However, I have idea about the asymptotics of the 2F12F1 term. Can anyone enlighten me on the asymptotics of




2F1left(m,m,1/2m,betaright)2F1left(m,m,1/2m,betaright)




when mm is large? In fact I tried mathematica and it seems 2F1left(m,m,1/2m,betaright)sim|4beta|m2F1left(m,m,1/2m,betaright)sim|4beta|m. Any reference on this issue?



Now given the above asymptotics is true, observe that the norm of HmHm under the weight rme2alpha2x2rme2alpha2x2 has the same exponent for all alphaalpha, including the original weight (alpha2=1/2alpha2=1/2). Is this a common phenomenon for orthogonal polynomials?

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