We consider a new idea for solving Tikhonov regularized discretized ill-posed problems. The optimization problem is formulated as a nonlinear least squares problems containing the Tikhonov regularization parameter λ. In order to find the size of the regularization parameter and attain good convergence in the optimization method we use the nonlinear Land a-curve. The nonlinear L-curve is a direc...

Regularization is used in order to obtain a reasonable estimate of the solution to an ill-posed inverse problem. One common form of regularization is to use a filter to reduce the influence of components corresponding to small singular values, perhaps using a Tikhonov least squares formulation. In this work, we break the problem into subproblems with narrower bands of singular values using spec...

We describe a parallel iterative least squares solver named LSRN that is based on random normal projection. LSRN computes the min-length solution to min x∈ℝ n ‖Ax - b‖2, where A ∈ ℝ m × n with m ≫ n or m ≪ n, and where A may be rank-deficient. Tikhonov regularization may also be included. Since A is involved only in matrix-matrix and matrix-vector multiplications, it can be a dense or sparse ma...

other areas. However, the spectral properties of the Laplace transform tend to complicate its numerical treatment; therefore, the closely related “truncated” Laplace transforms are often used in applications. In this dissertation, we construct efficient algorithms for the evaluation of the singular value decomposition (SVD) of such operators. The approach of this dissertation is somewhat simila...

other areas. However, the spectral properties of the Laplace transform tend to complicate its numerical treatment; therefore, the closely related “truncated” Laplace transforms are often used in applications. In this dissertation, we construct efficient algorithms for the evaluation of the singular value decomposition (SVD) of such operators. The approach of this dissertation is somewhat simila...

The global distribution of carbon sources and sinks is estimated from atmospheric CO2 measurements using an inverse method based on the Geophysical Fluid Dynamics Laboratory SKYHI atmospheric general circulation model. Applying the inverse model without any regularization yields unrealistically large CO2 fluxes in the tropical regions. We examine the use of three regularization techniques that ...

INTRODUCTION Electrical impedance tomography (EIT) is an emerging clinical tool for monitoring ventilation distribution in mechanically ventilated patients, for which many image reconstruction algorithms have been suggested. We propose an experimental framework to assess such algorithms with respect to their ability to correctly represent well-defined physiological changes. We defined a set of ...

Abstract This paper proposes a semi‐analytical and local meshless collocation method, the localized method of fundamental solutions (LMFS), to address three‐dimensional (3D) acoustic inverse problems in complex domains. The proposed approach is recently developed numerical scheme with potential being mathematically simple, numerically accurate, requiring less computational time storage. In LMFS...

Abstract. The truncated singular value decomposition is a popular solution method for linear discrete ill-posed problems. These problems are numerically underdetermined. Therefore, it can be beneficial to incorporate information about the desired solution into the solution process. This paper describes a modification of the singular value decomposition that permits a specified linear subspace t...