
A command to ask the selected Covariance object for the fraction of the total variance that is accounted for by the selected dimension(s).
The total variance is the sum of the diagonal elements of the covariance matrix C, i.e., its trace. The fraction is defined as:
Σ_{i=from..to} C_{ii} / Σ_{i=1..numberOfRows} C_{ii} 
© djmw, April 7, 2004