Review on Iterative methods, Preconditioning, Multigrid and Krylov methods Ecole des Mines de Paris, Sophia Antipolis [email protected] Used reference: Prof. Gilbert Strang, MIT Course Number 18.086, http://ocw.mit.edu/courses/mathematics/18-086-mathematical-methods-forengineers-ii-spring-2006/ Nab Raj Roshyara, KRYLOV SUBSPACE ITERATION, 2005 M. HESTENES AND E. STIEFEL, Methods of conjugate gradients for solving linear systems, J. Res. Nat. Bur. Stand., 49 (1952), pp. 409-436. W. ARNOLDI, The principle of minimized iterations in the solution of the matrix eigenvalue problem, Quart. Appl. Math., 9 (1951), pp. 17-29 Jonathan Richard Shewchuk, An Introduction to the Conjugate Gradient Method Without the Agonizing Pain, under the web http://www.cs.ucdavis.edu/ bai/ECS231/schewchukcgpaper.pdf Yousef Saad, Iterative methods for Sparse Linearsystems Henk A. van der Vorst, The article on \KRYLOV SUBSPACE ITERATION" of the journal Computing in Science and Engineering; 2000. P = diag ( A) P = triangular part of A = D + P = LappUapp How to decide? ek = M k e0 P = diag ( A) MultiGrid MultiGrid v-cycle for AX=b (fine to coarse) (coarse to fine) x = gmres(A,b) Step –1 We start inputting the matrix A, the vector b, and the initial guess x0. Then continue by computing the initial residual, r0, based on the initial input. The goal is to minimize this residual through the algorithm. b is the 2-norm of the residual and v1 is the normalized residual vector. This is the vector from which we build the Krylov subspace Step 2 : initializes an upper Hessenberg matrix Hm. This matrix has a direct relation to A. In fact if m equals n, and removing the last row of Hm, the relation is a similarity transformation, which preserves eigenvalues. Also the transformation matrix is Krylov basis composed of the vj vectors.

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