def cov_bias(x):
    return sp.cov(x, rowvar=0, bias=1)

def cov_nonbias(x):
    return sp.cov(x, rowvar=0, bias=0)

for data in [class2X, class2X[0:len(class2X)/2], class2X[0:len(class2X)/4]]:
    print "Difference: ", (sp.absolute(cov_bias(data) - cov_nonbias(data)))