On Tue, 8 Jul 2008, Mike Lawrence wrote:
#Let's try this again! This time the code is more sensible (curve range, same
sd value).
# Quick one hopefully. Shouldn't dnorm be returning the pdf?
No. See the documentation
?dnorm
especially what it says under 'Value'
Last time I
# checked,
# a probability shouldn't be greater than 1 as produced by:
curve(dnorm(x,0,.1),from=-.5,to=.5)
I do not see a probability that is greater than one here:
integrate(function(x) dnorm(x,0,.1),lower=-Inf,upper=Inf)
1 with absolute error < 6.1e-07
... looks like 1 to me.
#Shouldn't I be getting an axis more like that produced by:
f=function(x,m,s){
y=rep(NA,length(x))
for(i in 1:length(x)){
y[i]=integrate(
dnorm
, upper=x[i]+sqrt(.Machine$double.eps)
, lower=x[i]-sqrt(.Machine$double.eps)
, mean=m
, sd=s
) $value
}
return(y)
}
curve(f(x,0,.1),from=-.5,to=.5)
Well, what does this suggest?
integrate(function(x) f(x,0,.1),lower=-Inf,upper=Inf)
2.980232e-08 with absolute error < 2.6e-10
sqrt(.Machine$double.eps)*2
[1] 2.980232e-08
#If the latter code betrays a misunderstanding of what a pdf is, be gentle!
Well, the posting guide does ask you to do some homework before posting.
Nowadays, it is as easy. Google 'wiki probability density function' or
look in the reference in ?dnorm.
#Mike
--
Mike Lawrence
Graduate Student, Department of Psychology, Dalhousie University
www.memetic.ca
"The road to wisdom? Well, it's plain and simple to express:
Err and err and err again, but less and less and less."
- Piet Hein
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