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 Usage Arguments Details Value Author(s) References See Also Examples

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.

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dell(x, y, radius = 1, ...)

dellplus(x, y, ...)

`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`.

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

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

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,

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)