From maechler at stat.math.ethz.ch  Wed Jan 31 17:38:48 2007
From: maechler at stat.math.ethz.ch (maechler at stat.math.ethz.ch)
Date: Wed, 31 Jan 2007 17:38:48 +0100 (CET)
Subject: [Rd] Bug in 'pchisq' for x=0.0 (PR#9485)
Message-ID: <20070131163848.C04435A7AF@slim.kubism.ku.dk>

>>>>> "MN" == Michael Nothnagel <nothnagel at medinfo.uni-kiel.de>
>>>>>     on Wed, 31 Jan 2007 15:16:02 +0100 (CET) writes:

    MN> The function 'pchisq' from the 'stats' library gives a wrong result if the
    MN> argument equals exactly zero:

    MN> # Upper tail of central 1-df chi^2 distribution
    >> pchisq(1         , 1, ncp=0, lower.tail = F, log.p = FALSE)
    MN> [1] 0.3173105
    >> pchisq(0.5       , 1, ncp=0, lower.tail = F, log.p = FALSE)
    MN> [1] 0.4795001
    >> pchisq(0.01      , 1, ncp=0, lower.tail = F, log.p = FALSE)
    MN> [1] 0.9203443
    >> pchisq(0.0001    , 1, ncp=0, lower.tail = F, log.p = FALSE)
    MN> [1] 0.9920213
    >> pchisq(0.00000001, 1, ncp=0, lower.tail = F, log.p = FALSE)
    MN> [1] 0.9999202
    >> pchisq(0.00      , 1, ncp=0, lower.tail = F, log.p = FALSE)
    MN> [1] 0   ## Should be 1.0

    MN> The error occurred with R version 2.4.0 (windows) and version 2.3.1 (linux).

Yes, but both of these R versions are outdated.
The current version is 2.4.1
and there, the result *is* 1.

Regards,
Martin Maechler, ETH Zurich



[Rd] Bug in 'pchisq' for x=0.0 (PR#9485)
maechler at stat.math.ethz.ch