Spectral regularization method
= Spectral regularization method
A spectral regularization method applies a bounded scalar filter to the spectrum of $A^*A$. In a <singular system of a compact operator>, it has the form
$$
R_\alpha f=\sum_jg_\alpha(\sigma_j^2)\sigma_j\langle f,u_j\rangle v_j,
$$
where the filters approximate $1/\lambda$ while controlling amplification near $\lambda=0$.