# Ellipse in PCA with parameters "a" and "b"defined.

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## Ellipse in PCA with parameters "a" and "b"defined.

 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? Thanks Mary
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## Re: Ellipse in PCA with parameters "a" and "b"defined.

 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. Jim ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.
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## Re: Ellipse in PCA with parameters "a" and "b"defined.

 Ok... so, in my model my "a"  is built using the standard deviation of the first principal component and "b" with the second, so my "x" and "Y" should be :  PCA \$ scores [, 1], PCA \$ scores [, 2] but in this way I do not get out a confidence interval set on my parameters but many ellipses. Thanks Mary