[R] Plotting a smooth curve from predict

[Chuck Cleland]

Wilson, Andrew wrote:
> Probably a very simple query:
> 
> When I try to plot a curve from a fitted polynomial, it comes out rather
> jagged, not smooth like fitted curves in other stats software.  Is there
> a way of getting a smooth curve in R?
> 
> What I'm doing at the moment (for the sake of example) is:
> 
>> x <- c(1,2,3,4,5,6,7,8,9,10)
> 
>> y <- c(10,9,8,7,6,6.5,7,8,9,10)
> 
>> b <- data.frame(cbind(x,y))
> 
>> w <- gls(y ~ I(x)+I(x^2),correlation=corARMA(p=1),method="ML",data=b)
> 
>> plot(predict(w),type="l")

  Make predictions for more than 10 values of x:

x <- c(1,2,3,4,5,6,7,8,9,10)

y <- c(10,9,8,7,6,6.5,7,8,9,10)

b <- data.frame(cbind(x,y))

library(nlme)

w <- gls(y ~ I(x)+I(x^2), correlation=corARMA(p=1), method="ML", data=b)

plot(seq(1,10,len=100),
     predict(w, data.frame(x = seq(1,10, len=100))),
     xlab="x", ylab="Predicted y",
     type="l")

> Many thanks,
> 
> Andrew Wilson
> 
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-- 
Chuck Cleland, Ph.D.
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