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Iterative Methods for Sparse Linear Systems Second Edition

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CONTENTS vii<br />

5.1.2 Matrix Representation . . . . . . . . . . . . . . . 135<br />

5.2 General Theory . . . . . . . . . . . . . . . . . . . . . . . . . 137<br />

5.2.1 Two Optimality Results . . . . . . . . . . . . . . 137<br />

5.2.2 Interpretation in Terms of Projectors . . . . . . . 138<br />

5.2.3 General Error Bound . . . . . . . . . . . . . . . . 140<br />

5.3 One-Dimensional Projection Processes . . . . . . . . . . . . . 142<br />

5.3.1 Steepest Descent . . . . . . . . . . . . . . . . . . 142<br />

5.3.2 Minimal Residual (MR) Iteration . . . . . . . . . 145<br />

5.3.3 Residual Norm Steepest Descent . . . . . . . . . 147<br />

5.4 Additive and Multiplicative Processes . . . . . . . . . . . . . . 147<br />

6 Krylov Subspace <strong>Methods</strong> Part I 157<br />

6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 157<br />

6.2 Krylov Subspaces . . . . . . . . . . . . . . . . . . . . . . . . 158<br />

6.3 Arnoldi’s Method . . . . . . . . . . . . . . . . . . . . . . . . 160<br />

6.3.1 The Basic Algorithm . . . . . . . . . . . . . . . . 160<br />

6.3.2 Practical Implementations . . . . . . . . . . . . . 162<br />

6.4 Arnoldi’s Method <strong>for</strong> <strong>Linear</strong> <strong>Systems</strong> (FOM) . . . . . . . . . . 165<br />

6.4.1 Variation 1: Restarted FOM . . . . . . . . . . . . 167<br />

6.4.2 Variation 2: IOM and DIOM . . . . . . . . . . . 168<br />

6.5 GMRES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171<br />

6.5.1 The Basic GMRES Algorithm . . . . . . . . . . . 172<br />

6.5.2 The Householder Version . . . . . . . . . . . . . 173<br />

6.5.3 Practical Implementation Issues . . . . . . . . . . 174<br />

6.5.4 Breakdown of GMRES . . . . . . . . . . . . . . 179<br />

6.5.5 Variation 1: Restarting . . . . . . . . . . . . . . . 179<br />

6.5.6 Variation 2: Truncated GMRES Versions . . . . . 180<br />

6.5.7 Relations between FOM and GMRES . . . . . . . 185<br />

6.5.8 Residual smoothing . . . . . . . . . . . . . . . . 190<br />

6.5.9 GMRES <strong>for</strong> complex systems . . . . . . . . . . . 193<br />

6.6 The Symmetric Lanczos Algorithm . . . . . . . . . . . . . . . 194<br />

6.6.1 The Algorithm . . . . . . . . . . . . . . . . . . . 194<br />

6.6.2 Relation with Orthogonal Polynomials . . . . . . 195<br />

6.7 The Conjugate Gradient Algorithm . . . . . . . . . . . . . . . 196<br />

6.7.1 Derivation and Theory . . . . . . . . . . . . . . . 196<br />

6.7.2 Alternative Formulations . . . . . . . . . . . . . 200<br />

6.7.3 Eigenvalue Estimates from the CG Coefficients . . 201<br />

6.8 The Conjugate Residual Method . . . . . . . . . . . . . . . . 203<br />

6.9 GCR, ORTHOMIN, and ORTHODIR . . . . . . . . . . . . . . 204<br />

6.10 The Faber-Manteuffel Theorem . . . . . . . . . . . . . . . . . 206<br />

6.11 Convergence Analysis . . . . . . . . . . . . . . . . . . . . . . 208<br />

6.11.1 Real Chebyshev Polynomials . . . . . . . . . . . 209<br />

6.11.2 Complex Chebyshev Polynomials . . . . . . . . . 210<br />

6.11.3 Convergence of the CG Algorithm . . . . . . . . 214

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