Message-ID: <x265oujomh.fsf@biostat.ku.dk>
Date: 2003-05-02T00:16:35Z
From: Peter Dalgaard
Subject: qbeta hang (PR#2894)
In-Reply-To: <200305012044.h41Ki02b017789@pubhealth.ku.dk>
terra@gnome.org writes:
> Full_Name: Morten Welinder
> Version: 1.6.1
> OS: Solaris/sparc
> Submission from: (NULL) (65.213.85.144)
>
>
> qbeta(0.1, 1e-8, 0.5, TRUE, FALSE) seems to hang for me.
confirmed on 1.7.0 Solaris 9, gcc 3.0.3 (standard build, so -O2, I assume)
Morten: the gcc version is often crucial in these cases.
However, the exact same thing is happening on Linux. The immediate
cause is that n = fmax2(lneps/log(y), 4.0) gets large when y is in the
vicinity of 1-1e-8, so the loop in src/nmath/pbeta.c:101 gets a rather
high count. The algorithm isn't really stuck, it just takes a very
long time. On the fastest machine that I have available:
> system.time(qbeta(0.1, 1e-8, 0.5, TRUE, FALSE))
[1] 75.58 0.00 75.58 0.00 0.00
It's not really that surprising:
> pbeta(1e-5, 1e-8, 0.5,, TRUE, FALSE)
[1] 0.9999999
> pbeta(1e-10, 1e-8, 0.5,, TRUE, FALSE)
[1] 0.9999998
> pbeta(1e-200, 1e-8, 0.5,, TRUE, FALSE)
[1] 0.9999954
> pbeta(1e-309, 1e-8, 0.5,, TRUE, FALSE)
[1] 0.999993
> pbeta(1e-400, 1e-8, 0.5,, TRUE, FALSE)
[1] 0
and you're trying to solve pbeta(x, 1e-8, 0.5,, TRUE, FALSE) == 0.1
--
O__ ---- Peter Dalgaard Blegdamsvej 3
c/ /'_ --- Dept. of Biostatistics 2200 Cph. N
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk) FAX: (+45) 35327907