# [Rd] Re: [R] too large alpha or beta in dbeta ? (PR#643)

**maechler@stat.math.ethz.ch
**
maechler@stat.math.ethz.ch

*Fri, 25 Aug 2000 15:20:10 +0200 (MET DST)*

>>>>>* "TL" == Thomas Lumley <thomas@biostat.washington.edu> writes:
*
TL> On Thu, 24 Aug 2000, Troels Ring wrote:
>> Dear friends.
>>
>> Is this as expected ? Is alpha and beta too large simply ?
>>
>> > dbeta(.1,534,646)
>> [1] NaN
>> Warning message:
>> NaNs produced in: dbeta(x, shape1, shape2, log)
TL> well, it should work, but the correct answer is effectively zero.
TL> pbeta(.1,534,646) gives 3.6e-213
TL> Perhaps more worrying is
>> dbeta(.25,534,646)
TL> [1] Inf
yes.
and I see that it is one case where the log-density seems to be alright:
>* dbeta(.25,534,646,log=TRUE)
*[1] -109.939612
and also for the NaN case :
>* dbeta(.1,534,646, log=TRUE)
*[1] -480.725168
A workaround is using exp( log-density ), i.e.
exp(dbeta(x,a,b, log = TRUE)) :
Look at
>* plot(function(x) dbeta(x, 534,646, log = TRUE), n = 1001)
*or
>* plot(function(x)exp(dbeta(x, 534,646, log = TRUE)), n = 1001)
*
--
I'll have a look.
Martin
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