Smoothing and Regularization with Modified Sparse Approximate Inverses

Figure 7

Reconstruction error against the iteration for the deriv2 problem of [24] invoked with deriv2(2000,2) and affected by random noise of order 0.001% (a) and 0.01% (b), respectively. CG is compared to PCG using MSPAI with 𝑅3_𝐿1, 𝑅3_𝐿2, and 𝜌=10³ for the normal equations. MSPAI is symmetrized via 𝑀+𝑀^𝑇.

(a) Noise level 0.001%

(b) Noise level 0.01%