drawMahal {chemometrics} | R Documentation

## Draws ellipses according to Mahalanobis distances

### Description

For 2-dimensional data a scatterplot is made. Additionally, ellipses corresponding to certain Mahalanobis distances and quantiles of the data are drawn.

### Usage

    drawMahal(x, center, covariance, quantile = c(0.975, 0.75, 0.5, 0.25), m = 1000, lwdcrit = 1, ...)

### Arguments

`x` | numeric data frame or matrix with 2 columns
`center` | vector of length 2 with multivariate center of x
`covariance` | 2 by 2 covariance matrix of x
`quantile` | vector of quantiles for the Mahalanobis distance
`m` | number of points where the ellipses should pass through
`lwdcrit` | line width of the ellipses
`...` | additional graphics parameters, see `par`

### Details

For multivariate normally distributed data, a fraction of 1-quantile of data should be outside the ellipses. For center and covariance also robust estimators, e.g. from the MCD estimator, can be supplied.

### Value

A scatterplot with the ellipses is generated.

### Author(s)

Peter Filzmoser <P.Filzmoser@tuwien.ac.at>

### References

K. Varmuza and P. Filzmoser: Introduction to Multivariate Statistical Analysis in Chemometrics. CRC Press, Boca Raton, FL, 2009.

### See Also

`covMcd`

### Examples

    data(glass)
    data(glass.grp)
    x=glass[,c(2,7)]
    require(robustbase)
    x.mcd=covMcd(x)
    drawMahal(x,center=x.mcd$center,covariance=x.mcd$cov,quantile=0.975,pch=glass.grp)

[Package chemometrics version 0.6 Index]