[R] Plotting a smooth curve from predict

[Prof Brian Ripley]

You are using fitted() implicitly here, so you are not plotting a smooth 
curve but a set of fitted values.

You need to really predict at a suitable range of data points, e.g.

xx <- seq(1, 10, len=500)
plot(xx, predict(w, list(x=xx)), type="l")


BTW, why are you not using poly()?


On Tue, 31 Jul 2007, 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")
>
> Many thanks,
>
> Andrew Wilson
>
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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