>>>>> "TH" == Ted Harding <ted.hard...@manchester.ac.uk>
>>>>> on Mon, 30 Mar 2009 22:28:54 +0100 (BST) writes:
TH> On 30-Mar-09 20:37:51, Duncan Murdoch wrote:
>> On 3/30/2009 2:55 PM, (Ted Harding) wrote:
>>> On 30-Mar-09 18:40:03, Kjetil Halvorsen wrote:
>>>> With R 2.8.1 on ubuntu I get:
>>>>> gamma(-1)
>>>> [1] NaN
>>>> Warning message:
>>>> In gamma(-1) : NaNs produced
>>>>> lgamma(-1)
>>>> [1] Inf
>>>> Warning message:
>>>> value out of range in 'lgamma'
>>>>
>>>> Is'nt the first one right, and the second one (lgamma)
>>>> should also be NaN?
>>>> Kjetil
>>>
>>> That is surely correct! Since lim[x->(-1)+] gamma(x) = +Inf,
>>> while lim[x->(-1)-] gamma(x) = -Inf, at gamma(-1) one cannot
>>> choose between +Inf and -Inf, so surely is is NaN.
>>
>> But lgamma(x) is log(abs(gamma(x))), so it looks okay to me.
>>
>> Duncan Murdoch
TH> Oops, yes! That's what comes of talking off the top of my head
TH> (I don't think I've ever had occasion to evaluate lgamma(x)
TH> for negative x, so never consciously checked in ?lgamma).
TH> Thanks, Duncan!
Indeed.... as we all know, a picture can be worth a thousand words,
and a simple R call such as
plot(lgamma, -7, 0, n=1000)
would have saved many words, and notably spared us from
yet-another erroneous non-bug report.
Martin
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