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[Octave-bug-tracker] [bug #56453] chi2inv, gaminv, gammaincinv inaccurat

From: Jerry W. Lewis
Subject: [Octave-bug-tracker] [bug #56453] chi2inv, gaminv, gammaincinv inaccurate for small 1st argument
Date: Thu, 6 Jun 2019 22:49:09 -0400 (EDT)
User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:67.0) Gecko/20100101 Firefox/67.0

Follow-up Comment #1, bug #56453 (project octave):

Likely the issue is in part a poor starting value from which Newton's method
either diverges or converges very slowly.

It follows from Abramowitz & Stegun 26.4.6 that as p approaches zero,
chi2inv(p,df) approaches 2*[p*gamma(1+df/2)]^(2/df)


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