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 The inverse gamma function. tommy1729 Ultimate Fellow Posts: 1,365 Threads: 333 Joined: Feb 2009 05/11/2014, 08:28 PM Because of recent events here, I felt the need to talk about the inverse gamma function. Im talking about the entire approximation of exp^[1/2] and the Taylor coefficients being O ( 1/ Gamma( n (arc2sinh(n) - 1) ) ). Cleary from the viewpoint of numerical analysis it seems usefull to have a good approximation of the inverse gamma function. The functional inverse that is. Now my honesty forces me to quote the source of an intresting approximation of the inverse gamma function : David W Cantrell http://mathforum.org/kb/message.jspa?messageID=342552 In case that page gets removed I post the main formula here : A is the positive zero of the digamma function ( 1.4616... ) B = sqrt(2 pi) / e - Gamma(A). ( 0.0365... ) L(x) = ln( (x+c) / sqrt(2 pi) ) W(x) is the Lambert W function. ( the functional inverse of x exp(x)) Gamma^[-1](x) = approx = 1/2 + L(x)/W(L(x)/e) The error term goes to 0 as x goes to +oo. Together with the approximation for the Lambert W : LambertW(x) = ln(x) - ln(ln(x)) + ln(ln(x)) / ln(x) this gives a practical way to compute the inverse gamma function. I think there is also a page by wolfram about the inverse gamma but I cant find it ? ( And no, I dont mean the inverse regularized gamma or the statistical inverse gamma distribution ) I would like to see an integral representation of the inverse gamma function too. regards tommy1729 « Next Oldest | Next Newest »

 Messages In This Thread The inverse gamma function. - by tommy1729 - 05/11/2014, 08:28 PM RE: The inverse gamma function. - by JmsNxn - 05/11/2014, 10:12 PM RE: The inverse gamma function. - by tommy1729 - 05/12/2014, 11:06 PM RE: The inverse gamma function. - by JmsNxn - 05/13/2014, 02:18 PM

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