On Feb 21, 2012, at 11:43 AM, peter dalgaard wrote:
On Feb 21, 2012, at 16:36 , David Winsemius wrote:
It suggests you managed to send negative or infinite numbers to
dweibull, a distribution which only supports values when given
positive, finite numbers. Look at your data more closely.
Zeros are a common cause, too. For a < 1 (the shape parameter), the
Weibull density has a singularity at zero, and fitdistr() is not
tolerant of observations rounded to zero in such cases.
And that may be more correct than my guess. I see that the estimate
for the shape parameter from fitdistr is less than 1 and was
surprised that dweibull(-1, 2,2) does give a returned value of 0.
> dweibull(-.1, 0.61473436, 2.43536064 )
[1] 0
> dweibull(0, 0.61473436, 2.43536064 )
[1] Inf
> dweibull(0, 1.61473436, 2.43536064 )
[1] 0
--
David Winsemius, MD
West Hartford, CT
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