From: Brian Gough <bjg@network-theory.co.uk>
To: Frank Reininghaus <frank78ac@googlemail.com>
Cc: gsl-discuss@sourceware.org
Subject: Re: Examining bug #21838
Date: Sat, 16 Feb 2008 18:22:00 -0000 [thread overview]
Message-ID: <871w7crccq.wl%bjg@network-theory.co.uk> (raw)
In-Reply-To: <47B4C827.1040004@googlemail.com>
At Fri, 15 Feb 2008 00:00:55 +0100,
Frank Reininghaus wrote:
> I examined the first testcase: It seems that the origin of the NaN is in
> beta_cont_frac () in the source file cdf/beta_inc.c. The loop aborts
> after the maximum number of iterations because fabs (delta_frac - 1.0)
> does not get small enough, and NaN is returned.
>
> The funny thing is that I could influence this behaviour in a way I
> didn't expect:
That's interesting -- it looks like there is a problem with extended
precision making the result worse.
>
> (P - eP) [0] = nan, tolerance = 2.3283064365386963e-10
> (P - eP) [1] = nan, tolerance = 2.3283064365386963e-10
> (P - eP) [2] = nan, tolerance = 2.3283064365386963e-10
> (P - eP) [3] = 4.1520314247533996e-05, tolerance = 2.3283064365386963e-10
Here is a corrrection for the final value, it should be:
eP [3] = 0.9167386972447996480399
The results should make more sense with that. I'll commit that in the
test suite.
--
Brian Gough
next prev parent reply other threads:[~2008-02-16 18:22 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-02-14 23:01 Frank Reininghaus
2008-02-15 9:07 ` Jason Stover
2008-02-20 18:04 ` Brian Gough
2008-02-16 18:22 ` Brian Gough [this message]
2008-02-18 9:56 ` Brian Gough
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