[R] Ellipse in PCA with parameters "a" and "b"defined.

Jim Lemon jim at bitwrit.com.au
Tue Jan 22 04:46:20 CET 2013

On 01/22/2013 11:12 AM, mary wrote:
> Hi,
> I have to construct an ellipse interval region on a PCAbiplot, I have my
> parameters "a" and "b" and I would apply the formula:
> draw.ellipse(x, y, a = , b = )
> I have done a PCA on my data so I have my scores and loading for the first
> and second component, but my answer is what I have to choose as X and Y into
> the formula?
> if "a" and "b" are scalars or vectors should be x and y scalars or vectors
> too?
Hi Mary,
If this is draw.ellipse from the plotrix package, there should be an x 
and y corresponding to each pair of a and b. I was unable to work out 
which PCA biplot function you are using, so I am not sure whether the 
plots are drawn in base graphics. If not, you might have some problems 
with the x and y coordinates.


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