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Fig. 4

image

Convergence of the PCG solver of the CMB map-making problem for two different scanning strategy. Different types of lines correspond to different versions of the Toeplitz matrix used in the simulation, as described by the parameter fknee. Different colours correspond to the two different types of preconditioners: red for the standard block preconditioner MBD and green for the two-level preconditioner M2lvl,D whose coarse space ZD, is made of approximated eigenvectors corresponding to small eigenvalues λi of MBDA. dim(Z) denotes the number of columns in the deflation subspace operator ZD which is the number of eigenvalues with (Re | λi | <ϵtol = 0.3).

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