x1 covariance:
   0.09 1.7e-33 2.8e-33
1.7e-33    0.09 2.6e-17
2.8e-33 2.6e-17    0.01
x2 covariance:
   0.13 1.2e-18 6.1e-19
1.2e-18    0.17    0.02
6.1e-19    0.02    0.02
x3 covariance:
   0.17 8.6e-18 2.7e-18
8.6e-18    0.37    0.06
2.7e-18    0.06    0.03