dell: Calculate coordinates of a data ellipse In gmonette/spida: Collection of miscellaneous functions for mixed models etc. prepared for SPIDA 2009+ (development version)

Description

`dell` to calculates the coordinates of a 2D data ellipse (concentration ellipse) from (X, Y) variables.

`dellplus` can produce, in addition to the points of an ellipse, the conjugate axes corresponding to a `chol` or other decomposition and the surrounding parallelogram defined by these axes.

Usage

 ```1 2 3``` ```dell(x, y, radius = 1, ...) dellplus(x, y, ...) ```

Arguments

 `x, y` Either a two-column matrix or numeric vectors of the same length `radius` Radius of the ellipse-generating unit circle. The default, `radius=1` corresponds to a "standard" ellipse. `...` Other arguments passed down to `ell` or `ellplus`.

Details

These functions simply calculate the mean vector and covariance matrix and call `ell` or `ellplus`.

Value

Returns a 2-column matrix of (X,Y) coordinates suitable for drawing with `lines()`.

For `dellplus`, when more than one of the options `ellipse`, `diameters`, and `box` is `TRUE`, the different parts are separated by a row of `NA`.

Georges Monette

References

Monette, G. (1990). Geometry of Multiple Regression and Interactive 3-D Graphics. In Fox, J. & Long, S. (ed.) Modern Methods of Data Analysis, Sage Publications, 209-256.

`cell`, `ell`, `ellplus`,
 ```1 2 3 4 5 6 7 8 9``` ```data(Prestige) # from car attach(Prestige) fit.simple <- lm( prestige ~ education, Prestige) plot(prestige ~ education, type='p') lines(dell(education, prestige), col="blue", lwd=3) lines(bbox <- dellplus(education, prestige, box=TRUE)) lines(dellplus(education, prestige, diameter=TRUE, radius=2), col="gray") detach(Prestige) ```