# Re: [R] polygon error?

From: Mike Lawrence <Mike.Lawrence_at_dal.ca>
Date: Sat, 26 May 2007 08:06:14 -0300

polygon expects to be given the vertices, so if you want the area under the curve you'll want to include vertices at density=0

z <- pretty(c(-3,3), 100)
ht <- dnorm(z)
plot(z,ht, type="l")

zc <- 1.645
ht<-ht[z>zc]
z<-z[z>zc]

ht<-c(0,ht,0)
z<-c(z,z,z[length(z)])

polygon(z,ht,col='red')

On 26-May-07, at 7:34 AM, LL wrote:

> Hi.. I'm not sure why polygon returns an area above the standard
> normal curve.
>
> z <- pretty(c(-3,3), 100)
> ht <- dnorm(z)
> data <- data.frame(z=z, ht=ht)
> zc <- 1.645
> plot(data, type="l")
> lines(data)
> t <- subset(data, z>zc)
> polygon(t, col="red")
>
> Thanks,
> Lance
>
>
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>
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```--
Mike Lawrence
Graduate Student, Department of Psychology, Dalhousie University

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