[GRASS-user] Help with i.pca output

[William Hudspeth]

Hello,

I have been employing GRASS 6.2 to do Principal Components Analysis
(PCA) on a series of images using the i.pca command. The output of
eigenvectors looks like the following:

( 0.55 0.78 0.28 ) 
( -0.17 -0.22 0.96 ) 
( 0.82 -0.58 0.01 ) 

However, lacking training in matrix algebra, I am unsure about how to
generate eigen values and percent variance explained by the different
principal components from the eigen vectors. The GRASS 6.4 documentation
for i.pca indicates that this alternative information is included in the
new output (see the documentation example below):

r.info -h spot_pca.1
   Eigen values, (vectors), and [percent importance]:
   PC1   1170.12 ( -0.63 -0.65 -0.43 ) [ 88.07% ]
   PC2    152.49 (  0.23  0.37 -0.90 ) [ 11.48% ]
   PC3      6.01 (  0.75 -0.66 -0.08 ) [  0.45% ]

After installing GRASS 6.4, however, the output claims to be eigen values, 
but looks more like eigen vectors as for GRASS 6.2:

( 0.37 0.46 0.81 ) 
( -0.50 -0.63 0.59 ) 
( 0.78 -0.63 -0.01 )

I would appreciate any help on interpreting these values, or knowing why
the output of i.pca in GRASS 6.4 doesn't match what is in the
documentation. Ultimately, I am only trying to get at the percent
variance for each principal component so that I can proceed with
supervised and unsupervised classification of my images.

Thanks much,

William