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Subsection 9.2.3: FGMRES Up Section 9.2: Configuring Linear Solvers Subsection 9.2.5: BoomerAMG

### 9.2.4 CG

This iterative linear solver, from the MKL library, implements the Conjugate Gradient algorithm, which is an efficient Krylov-based iterative solution strategy for symmetric systems. It requires several configuration parameters, listed below, and only works with unsymmetric matrices. In the table below, N refers to the number of equations.
 parameter description default max_iter The maximum number of iterations min(N,150) tol relative residual tolerance 1e-6 print_level The amount of information printed (0,1, or 2) 0 pc_left The left preconditioner (none)
Subsection 9.2.3: FGMRES Up Section 9.2: Configuring Linear Solvers Subsection 9.2.5: BoomerAMG