synlik (version 0.1.1)

robCov: Robust covariance matrix estimation

Description

Obtains a robust estimate of the covariance matrix of a sample of multivariate data, using Campbell's (1980) method as described on p231-235 of Krzanowski (1988).

Usage

robCov(sY, alpha = 2, beta = 1.25)

Arguments

sY

A matrix, where each column is a replicate observation on a multivariate r.v.

alpha

tuning parameter, see details.

beta

tuning parameter, see details.

Value

A list where:

• Ea square root of the inverse covariance matrix. i.e. the inverse cov matrix is t(E)%*%E;

• half.ldet.VHalf the log of the determinant of the covariance matrix;

• mYThe estimated mean;

• sdThe estimated standard deviations of each variable.

Details

Campbell (1980) suggests an estimator of the covariance matrix which downweights observations at more than some Mahalanobis distance d.0 from the mean. d.0 is sqrt(nrow(sY))+alpha/sqrt(2). Weights are one for observations with Mahalanobis distance, d, less than d.0. Otherwise weights are d.0*exp(-.5*(d-d.0)^2/beta)/d. The defaults are as recommended by Campbell. This routine also uses pre-conditioning to ensure good scaling and stable numerical calculations.

References

Krzanowski, W.J. (1988) Principles of Multivariate Analysis. Oxford. Campbell, N.A. (1980) Robust procedures in multivariate analysis I: robust covariance estimation. JRSSC 29, 231-237.

Examples

# NOT RUN {
p <- 5;n <- 100
Y <- matrix(runif(p*n),p,n)
robCov(Y)
# }