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 -- View this message in context: http://r.789695.n4.nabble.com/Ellipse-in-PCA-with-parameters-a-and-b-defined-tp4656215.html Sent from the R help mailing list archive at Nabble.com.
Ellipse in PCA with parameters "a" and "b"defined.
5 messages · Jim Lemon, David L Carlson, mary
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
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 -- View this message in context: http://r.789695.n4.nabble.com/Ellipse-in-PCA-with-parameters-a-and-b-defined-tp4656215p4656242.html Sent from the R help mailing list archive at Nabble.com.
Try x <- mean(PCA$scores[,1]) and y <- mean(PCA$scores[,2]) which should be the same as x <- 0, y <- 0 within rounding error. ---------------------------------------------- David L Carlson Associate Professor of Anthropology Texas A&M University College Station, TX 77843-4352
-----Original Message----- From: r-help-bounces at r-project.org [mailto:r-help-bounces at r- project.org] On Behalf Of mary Sent: Tuesday, January 22, 2013 3:40 AM To: r-help at r-project.org Subject: Re: [R] 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 -- View this message in context: http://r.789695.n4.nabble.com/Ellipse-in- PCA-with-parameters-a-and-b-defined-tp4656215p4656242.html Sent from the R help mailing list archive at Nabble.com.
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thank you David, it was my first idea, but i don't know if it is right statistically speaking!!! -- View this message in context: http://r.789695.n4.nabble.com/Ellipse-in-PCA-with-parameters-a-and-b-defined-tp4656215p4656274.html Sent from the R help mailing list archive at Nabble.com.