$ \# $ of outer iteration | |||
Method | 0th | 1st | 3rd |
$ \ell_{1} $-IEKF $ \ell_{0.5} $-IEKF $ \ell_{1} $-IEKF-SL $ \ell_{0.5} $-IEKF-SL |
0.238 0.238 0.205 0.205 |
0.168 0.148 0.141 0.132 |
0.094 0.057 0.067 0.037 |
This paper introduces a computational framework to incorporate flexible regularization techniques in ensemble Kalman methods, generalizing the iterative alternating scheme to nonlinear inverse problems. The proposed methodology approximates the maximum a posteriori (MAP) estimate of a hierarchical Bayesian model characterized by a conditionally Gaussian prior and generalized gamma hyperpriors. Suitable choices of hyperparameters yield sparsity-promoting regularization. We propose an iterative algorithm for MAP estimation, which alternates between updating the unknown with an ensemble Kalman method and updating the hyperparameters in the regularization to promote sparsity. The effectiveness of our methodology is demonstrated in several computed examples, including compressed sensing and subsurface flow inverse problems.
Citation: |
Figure 4. Example in Subsection 4.2. Red: target function to recover. Blue: $ \ell_p $-IEKF recovery. Top row: $ \ell_{1} $-IEKF. Bottom row: $ \ell_{0.5} $-IEKF. Left column: vanilla IEKF. Middle column: $ \ell_p $-IEKF after one outer iteration. Right column: $ \ell_p $-IEKF after three outer iterations. Shaded: 2.5/97.5 percentile of the recovery
Figure 5. Example in Subsection 4.2. Red: target function to recover. Blue: $ \ell_p $-IEKF-SL recovery. Top row: $ \ell_{1} $-IEKF-SL. Bottom row: $ \ell_{0.5} $-IEKF-SL. Left column: vanilla IEKF-SL. Middle column: $ \ell_p $-IEKF-SL after one outer iteration. Right column: $ \ell_p $-IEKF-SL after three outer iterations. Shaded: 2.5/97.5 percentile of the recovery
Figure 6. Parameter recovery for 2D-elliptic inverse problem based on $ \ell_{1} $/$ \ell_{0.5} $-IEKF. Red: Truth. Blue: $ \ell_p $-IEKF estimate. Left column: vanilla (non-regularized) IEKF. Middle column: $ \ell_p $-IEKF after three outer iterations. Right column: $ \ell_p $-IEKF after six outer iterations. Shaded: elementwise 2.5/97.5 percentile for parameter estimate
Figure 7. Parameter recovery for 2D-elliptic inverse problem based on $ \ell_{1} $/$ \ell_{0.5} $-IEKF-SL. Red: Truth. Blue: $ \ell_p $-IEKF-SL estimate. Left column: vanilla (non-regularized) IEKF-SL. Middle column: $ \ell_p $-IEKF-SL after three outer iterations. Right column: $ \ell_p $-IEKF-SL after six outer iterations. Shaded: elementwise 2.5/97.5 percentile for parameter estimate
Table 4.1.
$ \# $ of outer iteration | |||
Method | 0th | 1st | 3rd |
$ \ell_{1} $-IEKF $ \ell_{0.5} $-IEKF $ \ell_{1} $-IEKF-SL $ \ell_{0.5} $-IEKF-SL |
0.238 0.238 0.205 0.205 |
0.168 0.148 0.141 0.132 |
0.094 0.057 0.067 0.037 |
Table 4.2. Average width of credible intervals for recovery
$ \# $ of outer iteration | |||
Method | 0th | 1st | 3rd |
$ \ell_{1} $-IEKF $ \ell_{0.5} $-IEKF $ \ell_{1} $-IEKF-SL $ \ell_{0.5} $-IEKF-SL |
3.678 3.678 4.660 4.660 |
5.371 4.945 3.649 3.060 |
4.228 2.959 2.898 2.400 |
Table 4.3.
$ \# $ of outer iteration | |||
Method | 0th | 3rd | 6th |
$ \ell_{1} $-IEKF $ \ell_{0.5} $-IEKF $ \ell_{1} $-IEKF-SL $ \ell_{0.5} $-IEKF-SL |
0.030 0.030 0.030 0.030 |
0.014 0.004 0.020 0.008 |
0.012 0.002 0.014 0.007 |
Table 4.4. Average width of credible intervals for recovery
$ \# $ of outer iteration | |||
Method | 0th | 3rd | 6th |
$ \ell_{1} $-IEKF $ \ell_{0.5} $-IEKF $ \ell_{1} $-IEKF-SL $ \ell_{0.5} $-IEKF-SL |
1.211 1.211 1.399 1.399 |
0.198 0.055 0.259 0.041 |
0.211 0.017 0.169 0.007 |
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Leftmost: Newton iteration. Middle-left: continuum Newton trajectory. Middle-right: ensemble Kalman iteration. Rightmost: continuum ensemble trajectory
Parameter estimation and uncertainty quantification in linear example with
Left:
Example in Subsection 4.2. Red: target function to recover. Blue:
Example in Subsection 4.2. Red: target function to recover. Blue:
Parameter recovery for 2D-elliptic inverse problem based on
Parameter recovery for 2D-elliptic inverse problem based on