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Iterative Methods for Sparse Linear Systems Second Edition

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CONTENTS ix<br />

10.3 ILU Factorization Preconditioners . . . . . . . . . . . . . . . 301<br />

10.3.1 Incomplete LU Factorizations . . . . . . . . . . . 301<br />

10.3.2 Zero Fill-in ILU (ILU(0)) . . . . . . . . . . . . . 307<br />

10.3.3 Level of Fill and ILU(p) . . . . . . . . . . . . . . 311<br />

10.3.4 Matrices with Regular Structure . . . . . . . . . . 315<br />

10.3.5 Modified ILU (MILU) . . . . . . . . . . . . . . . 319<br />

10.4 Threshold Strategies and ILUT . . . . . . . . . . . . . . . . . 321<br />

10.4.1 The ILUT Approach . . . . . . . . . . . . . . . . 321<br />

10.4.2 Analysis . . . . . . . . . . . . . . . . . . . . . . 323<br />

10.4.3 Implementation Details . . . . . . . . . . . . . . 325<br />

10.4.4 The ILUTP Approach . . . . . . . . . . . . . . . 327<br />

10.4.5 The ILUS Approach . . . . . . . . . . . . . . . . 330<br />

10.4.6 The Crout ILU Approach . . . . . . . . . . . . . 332<br />

10.5 Approximate Inverse Preconditioners . . . . . . . . . . . . . . 336<br />

10.5.1 Approximating the Inverse of a <strong>Sparse</strong> Matrix . . 337<br />

10.5.2 Global Iteration . . . . . . . . . . . . . . . . . . 337<br />

10.5.3 Column-Oriented Algorithms . . . . . . . . . . . 339<br />

10.5.4 Theoretical Considerations . . . . . . . . . . . . 341<br />

10.5.5 Convergence of Self Preconditioned MR . . . . . 343<br />

10.5.6 Approximate Inverses via bordering . . . . . . . . 346<br />

10.5.7 Factored inverses via orthogonalization: AINV . . 348<br />

10.5.8 Improving a Preconditioner . . . . . . . . . . . . 349<br />

10.6 Reordering <strong>for</strong> ILU . . . . . . . . . . . . . . . . . . . . . . . 350<br />

10.6.1 Symmetric permutations . . . . . . . . . . . . . . 350<br />

10.6.2 Nonsymmetric reorderings . . . . . . . . . . . . . 352<br />

10.7 Block Preconditioners . . . . . . . . . . . . . . . . . . . . . . 354<br />

10.7.1 Block-Tridiagonal Matrices . . . . . . . . . . . . 354<br />

10.7.2 General Matrices . . . . . . . . . . . . . . . . . . 356<br />

10.8 Preconditioners <strong>for</strong> the Normal Equations . . . . . . . . . . . 356<br />

10.8.1 Jacobi, SOR, and Variants . . . . . . . . . . . . . 357<br />

10.8.2 IC(0) <strong>for</strong> the Normal Equations . . . . . . . . . . 357<br />

10.8.3 Incomplete Gram-Schmidt and ILQ . . . . . . . . 360<br />

11 Parallel Implementations 369<br />

11.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 369<br />

11.2 Forms of Parallelism . . . . . . . . . . . . . . . . . . . . . . . 370<br />

11.2.1 Multiple Functional Units . . . . . . . . . . . . . 370<br />

11.2.2 Pipelining . . . . . . . . . . . . . . . . . . . . . 370<br />

11.2.3 Vector Processors . . . . . . . . . . . . . . . . . 371<br />

11.2.4 Multiprocessing and Distributed Computing . . . 371<br />

11.3 Types of Parallel Architectures . . . . . . . . . . . . . . . . . 371<br />

11.3.1 Shared Memory Computers . . . . . . . . . . . . 372<br />

11.3.2 Distributed Memory Architectures . . . . . . . . 374<br />

11.4 Types of Operations . . . . . . . . . . . . . . . . . . . . . . . 376

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