[R] pnorm, relative accuracy in the tails

[Ole Christensen]

Dear R people

The function below should be decreasing, convex, and tend to zero when x
tends to infinity.

curve((1-pnorm(x))/dnorm(x),from=0, to=9)

>From the plot we see that for x between 8.0 and 8.3 the function is
fluctuating.

As far as I understand, this is due to the function pnorm() not being
sufficiently accurate in the tails. 
I am using pnorm() in a way that has probably not been intended. 
So I guess this should not be considered a bug (??)

The function can also be written as 1/lambda(x) where lambda(x) is the
hazard rate for the normal distribution. Is there a way to calculate
lambda(x) without using pnorm() ?

Any help would be appreciated.

Cheers

Ole Christensen


-- 
Ole F. Christensen
Department of Mathematics and Statistics
Fylde College, Lancaster University 
Lancaster, LA1 4YF, England
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