[R] Problem with Princurve

[Gavin Simpson]

On Thu, 2011-05-19 at 06:43 -0700, guy33 wrote:
> Hey all,
> 
> I can't seem to get the princurve package to produce correct results, even
> in the simplest cases.  For example, if you just generate a 1 period
> noiseless sine wave, and ask for the principal curve and plot, the returned
> curve is clearly wrong (doesn't follow the sine wave).  Here's my code:
> 
> library(princurve)
> x <- runif(1000,0,2*pi); x <- cbind(x/(2*pi), sin(x))
> fit1 <- principal.curve(x, plot = TRUE)
> 
> Anyone have any suggestions?  If you run this code, do you get the correct
> principal curve?

How about specifying some useful starting points?

fit1 <- principal.curve(x, plot = TRUE, trace = TRUE, maxit = 100,
                        start = cbind(sort(x[,1]), rep(1, nrow(x))))

And we need a few more iterations before convergence here. Starting from
the first principal component for example might give useful starting
points.

HTH

G

> Any help would be really appreciated!
> -guy33 
> 
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