R help - Sep 2009 - Ellipse: Major Axis Minor Axis

I have a matrix(3000x2) of numbers and I have plotted a scatterplot
(defined in the ``car'' library.)

scatterplot(r$V1,r$V2,ellipse=TRUE)

The ellipse plotted is an error ellipse.

I want the find the major(semi), minor(semi) minor axis length of this
ellipse.
Does anybody know how to do it?

I can get the center of this ellipse using the cov.trob function
(defined in ``MASS'' library),
and with some formula, also the Angle of Rotation of the error
ellipse.

Any help on finding the major, minor axis lenght of the ellipse
greatly appreciated!!

Thank you!

Vishal.

Vishal <vishalps <at> gmail.com> writes:
> 
> I have a matrix(3000x2) of numbers and I have plotted a scatterplot
> (defined in the ``car'' library.)
> 
> scatterplot(r$V1,r$V2,ellipse=TRUE)
> 
> The ellipse plotted is an error ellipse.
> 
> I want the find the major(semi), minor(semi) minor axis length of this
> ellipse.
> 
If you have the ellipse from cov.trob(), then you could do like this

sqrt(eigen(cov.trob(mydataforellipse)$cov)$values)

Cheers, Jari Oksanen