Hi,
I'm using the R library(car) to draw confidence/prediction ellipses in a
scatterplot.
>From what i understood  the ellipse() function return an ellipse based
parameters:  shape, center,  radius .
If i read  dataEllipse() function i can see how these parameters are
calculated for a confidence ellipse.

ibrary(car)

a=c(12,12,4,5,63,63,23)
b=c(13,15,7,10,73,83,43)

v <- cov.trob(cbind(a, b))
shape <- v$cov
center <- v$center

radius <- sqrt(2 * qf(0.95, 2, length(a) - 1))   # radius <- sqrt(dfn *
qf(level, dfn, dfd))

conf.elip = ellipse(center, shape, radius,draw = F)
plot(conf.elip, type='l')
points(a,b)

My question is how I can calculate shape, center and radius  to obtain a
prediction ellipses rather than a confidence ellipse?
Thanks in Advance
Giuseppe

-- 
Giuseppe Amatulli
Web: www.spatial-ecology.net

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