In this work we illustrate a number of properties of the Born approximation in the three-dimensional Calderón inverse conductivity problem by numerical experiments. The results are based on an explicit representation formula for the Born approximation recently introduced by the authors. We focus on the particular case of radial conductivities in the ball $ B_R \subset \mathbb{R}^3 $ of radius $ R $, in which the linearization of the Calderón problem is equivalent to a Hausdorff moment problem. We give numerical evidences that the Born approximation is well defined for $ L^{\infty} $ conductivities, and present a novel numerical algorithm to reconstruct a radial conductivity from the Born approximation under a suitable smallness assumption. We also show that the Born approximation has depth-dependent uniqueness and approximation capabilities depending on the distance (depth) to the boundary $ \partial B_R $. We then investigate how increasing the radius $ R $ affects the quality of the Born approximation, and the existence of a scattering limit as $ R\to \infty $. Similar properties are also illustrated in the inverse boundary problem for the Schrödinger operator $ -\Delta +q $, and strong recovery of singularity results are observed in this case.
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Experiment 1: A step conductivity and its Born approximation (left), and a comparison of their Fourier transforms (right). Lower simulations correspond to a conductivity closer to the reference conductivity
Experiment 2: Three different conductivities that coincide in the interval
Experiment 3: Scattering limit. A conductivity
Experiment 4: Born approximations (left) and their Fourier transform (right) for smooth conductivities with different sizes
Experiment 5: Born approximations (left) and their Fourier transform (right) for a step conductivity with noisy data
Experiment 6: Born approximation of a step potentials (left) and its Fourier transform (right), that illustrate the recovery of singularities property
Experiment 7: average error distribution of the Born approximation,
Experiment 8: Born approximation of a potential which is zero in a neighborhood of
Experiment 9: Born approximation of a potential (left) and its Fourier transform (right) when we consider domains with
Experiment 10: Born approximation of a negative potential (left) and its Fourier transform (right)
Experiment 11: Approximation of a Lipschitz conductivity (left simulation) and a smooth one (right simulation) by the iterative algorithm (9)
Experiment 11: