Iterated Tikhonov spectral filter ($g_k(\lambda )=[1-(1+\tau \lambda {)}^{-k}]/\lambda$)

The implicit iteration $(I+\tau K^{\ast }K)u_{k+1}=u_k+\tau K^{\ast }f$, starting from zero, multiplies each data singular vector by $[1-(1+\tau {\sigma }^2{)}^{-k}]/\sigma$. Its operator norm is at most $\sqrt{k\tau }$.