Smoothing and Regularization with Modified Sparse Approximate Inverses

Figure 8

Reconstruction error against the iteration for the blur problem of [24] invoked with blur(150,4,1) and affected by random noise of order 0.01% (a) and 1% (b), respectively. CG is compared to CG using normal equations, PCG using MSPAI with 𝑅5_𝐺1, 𝑅5_𝐺2, 𝑅5_𝐺3, and PCG using MSPAI for normal equations with 𝜌=1. We use 𝑀+𝑀^𝑇 as preconditioner within PCG(𝐺) and 𝑀^𝑇𝑀 for PCG(𝐺^𝑇𝐺).

(a) Noise level 0.01%

(b) Noise level 1%