[Rd] dgamma error condition?

Ben Bolker bolker at zoo.ufl.edu
Tue Nov 8 15:17:33 CET 2005

   thanks.  would you like a patch?
(seems easy enough but I thought I'd offer)
looks like library/stats/R/distn.R and
nmath/rgamma.c need fixing; looks like
qgamma may not check for scale<0 in C
code either ...

   Ben Bolker

Prof Brian Ripley wrote:
> On Fri, 4 Nov 2005, Ben Bolker wrote:
>>   There's an apparent inconsistency between the
>> behavior of d(pqr)gamma and other distribution
>> functions for "bad" parameter values.  Specifically,
>> most distributions give NaN and a warning for bad
>> parameters (e.g. probabilities <0 or >1).  In contrast,
>> d(pqr)gamma actually gives an error and stops when shape<0.
>> I don't see why it has to be this way -- the internal
>> C code is set up to detect shape<0 (or scale<0) and
>> return NaN and a warning, and none of the other
>> distribution functions in that bit of the code have
>> similar behavior.
>>   It would seem more consistent (and would be more
>> convenient for me -- the error-instead-of-warning
>> is making me have to jump through additional hoops)
>> if dgamma just returned NaN and a warning.
>>    Any thoughts?
> No one has come up with any, so let us remove the errors in R-devel.
> Note that rgamma is not protected at C level: try rgamma(10, -2), or 
> (worse) rgamma(10, -20)  after removing the stop() call.

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