[R] rgamma with negative shape and scale parameters works?

[Peter Dalgaard BSA]

Faheem Mitha <faheem at email.unc.edu> writes:

> Dear R people,
> 
> This is a possibly silly question, but the rgamma function takes the shape
> and scale arguments and simulates gamma rvs corresponding to those values,
> right? But the shape and scale parameters have to be positive, right?
> However, rgamma quite happily returns to me values for negative values of
> shape and scale, and in some cases returns negative values eg.
> 
> > rgamma(1, 1, -1)
> [1] -1.011081
> > rgamma(1, -1, -1)
> [1] -1.710464
> > rgamma(1, -1, 1)
> [1] 2.058639

Most likely, it is a bug(let). Calculating dgamma(rgamma(... with the
same parameters give NaN. 

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
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