[GRASSLIST:2932] i.gensigset & signaturefiles

Hi,
this is a question concerning i.gensigset:
I generated a signaturefile containing the
following classtype; I suppose covar shows
the covariance matrix but I don't understand
why there are negative values (theoretically
a "normal" covariance matrix should not
include negative values ?).

classtype: 1
subclass:
  pi: 1.000000
  means: 28.729358 21.571101 71.933486 8.634557
  covar:
    46.942043 7.925971 132.644078 -0.054562
    7.925971 16.780113 -2.244889 -0.098634
    132.644078 -2.244889 541.903068 0.468048
    -0.054562 -0.098634 0.468048 1.889387

Thanxx L