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Re: [Help-gsl] Bug in implementing Kummer's U?


From: Brian Gough
Subject: Re: [Help-gsl] Bug in implementing Kummer's U?
Date: Tue, 7 Feb 2006 11:45:48 +0000

George Japaridze writes:
 > U(a, 0.5 ,z) = sqrt(pi) ( 1F1(a, 0.5, z)/gamma(a+0.5) - 2*sqrt(z)*1F1 
 > (a+0.5, 1.5, z)/gamma(a) )           (1)

The RHS is a difference of two nearly equal large numbers for large z
so you are going to get a huge cancellation error just from the
subtraction.

-- 
Brian Gough

Network Theory Ltd,
Publishing the GSL Manual --- http://www.network-theory.co.uk/gsl/manual/




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