Make an ellipse
A generic function returning an ellipse or other outline of a confidence region for two parameters.
ellipse(x, ...)
## Default S3 method:
ellipse(x, scale = c(1, 1), centre = c(0, 0), level = 0.95,
t = sqrt(qchisq(level, 2)), which = c(1, 2), npoints = 100, ...)x |
An object. In the default method the parameter |
... |
Descendant methods may require additional parameters. |
scale |
If |
centre |
The centre of the ellipse will be at this position. |
level |
The confidence level of a pairwise confidence region. The default is 0.95, for a 95% region. This is used to control the size of the ellipse being plotted. A vector of levels may be used. |
t |
The size of the ellipse may also be controlled by specifying the value of a t-statistic on its boundary. This defaults to the appropriate value for the confidence region. |
which |
This parameter selects which pair of variables from the matrix will be plotted. The default is the first 2. |
npoints |
The number of points used in the ellipse. Default is 100. |
The default method uses the
(cos(theta + d/2), cos(theta - d/2)) parametrization of an ellipse, where
cos(d) is the correlation of the parameters.
An npoints x 2 matrix is returned with columns named according to the
row names of the matrix x (default 'x' and 'y'), suitable
for plotting.
Murdoch, D.J. and Chow, E.D. (1996). A graphical display of large correlation matrices. The American Statistician 50, 178-180.
# Plot an ellipse corresponding to a 95% probability region for a # bivariate normal distribution with mean 0, unit variances and # correlation 0.8. plot(ellipse(0.8), type = 'l')
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