x1 covariance:
       0.09     1.1e-47     5.7e-33
    1.1e-47        0.09     1.9e-17
    5.7e-33     1.9e-17        0.01
x2 covariance:
       0.13     4.7e-18     2.4e-18
    4.7e-18        0.17        0.02
    2.4e-18        0.02        0.02
x3 covariance:
       0.17     2.7e-17     8.4e-18
    2.7e-17        0.37        0.06
    8.4e-18        0.06        0.03