A Subspace Preconditioned LSQR Gauss-Newton Method with a Constrained Line Search Path Applied to 3D Biomedical Microwave Imaging

Figure 2

The singular value spectra of the matrix without regularization () and with regularization () for a generic inverse scattering problem with 2000 permittivity unknowns. The spectrum of the matrix where contains the truncated 3D discrete cosine basis corresponding to .