[R] qt with df<1 (repost)

[Prof Brian Ripley]

Please do RTFM, for the help says

       df: degrees of freedom (> 0, maybe non-integer).  'df = Inf' is
           allowed.  For 'qt' only values of at least one are currently
           supported.

On Sun, 12 Oct 2008, Enrico Rossi wrote:

> Sorry about the html-formatted message. Here it is again in plain text.
>
> Hello,
>
> The function qt returns NaN for degrees of freedom <1. For example:
>
>> qt(0.5,0.5)
> [1] NaN
> Warning message:
> In qt(p, df, lower.tail, log.p) : NaNs produced
>
> But qt(0.5,0.5) should be 0, since the distribution is symmetric.
>
>> pt(0,0.5)
> [1] 0.5
>
> It actually fails with any value, as long as df<1.
> Is this a bug, or is there some fundamental reason why this cannot be
> computed?

Neither ....

>
> Thank you,
> Enrico

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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