Steepest Descent and Conjugate Gradient Methods with Variable Preconditioning

We analyze the conjugate gradient (CG) method with variable preconditioning for solving a linear system with a real symmetric positive definite (SPD) matrix of coefficients $A$. We assume that the preconditioner is SPD on each step, and that the condition number of the preconditioned system matrix i...

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Published in:SIAM journal on matrix analysis and applications Vol. 29; no. 4; pp. 1267 - 1280
Main Authors: Knyazev, Andrew V., Lashuk, Ilya
Format: Journal Article
Language:English
Published: Philadelphia, PA Society for Industrial and Applied Mathematics 01.01.2007
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ISSN:0895-4798, 1095-7162
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Abstract We analyze the conjugate gradient (CG) method with variable preconditioning for solving a linear system with a real symmetric positive definite (SPD) matrix of coefficients $A$. We assume that the preconditioner is SPD on each step, and that the condition number of the preconditioned system matrix is bounded above by a constant independent of the step number. We show that the CG method with variable preconditioning under this assumption may not give improvement, compared to the steepest descent (SD) method. We describe the basic theory of CG methods with variable preconditioning with the emphasis on "worst case" scenarios, and provide complete proofs of all facts not available in the literature. We give a new elegant geometric proof of the SD convergence rate bound. Our numerical experiments, comparing the preconditioned SD and CG methods, not only support and illustrate our theoretical findings, but also reveal two surprising and potentially practically important effects. First, we analyze variable preconditioning in the form of inner-outer iterations. In previous such tests, the unpreconditioned CG inner iterations are applied to an artificial system with some fixed preconditioner as a matrix of coefficients. We test a different scenario, where the unpreconditioned CG inner iterations solve linear systems with the original system matrix $A$. We demonstrate that the CG-SD inner-outer iterations perform as well as the CG-CG inner-outer iterations in these tests. Second, we compare the CG methods using a two-grid preconditioning with fixed and randomly chosen coarse grids, and observe that the fixed preconditioner method is twice as slow as the method with random preconditioning.
AbstractList We analyze the conjugate gradient (CG) method with variable preconditioning for solving a linear system with a real symmetric positive definite (SPD) matrix of coefficients $A$. We assume that the preconditioner is SPD on each step, and that the condition number of the preconditioned system matrix is bounded above by a constant independent of the step number. We show that the CG method with variable preconditioning under this assumption may not give improvement, compared to the steepest descent (SD) method. We describe the basic theory of CG methods with variable preconditioning with the emphasis on "worst case" scenarios, and provide complete proofs of all facts not available in the literature. We give a new elegant geometric proof of the SD convergence rate bound. Our numerical experiments, comparing the preconditioned SD and CG methods, not only support and illustrate our theoretical findings, but also reveal two surprising and potentially practically important effects. First, we analyze variable preconditioning in the form of inner-outer iterations. In previous such tests, the unpreconditioned CG inner iterations are applied to an artificial system with some fixed preconditioner as a matrix of coefficients. We test a different scenario, where the unpreconditioned CG inner iterations solve linear systems with the original system matrix $A$. We demonstrate that the CG-SD inner-outer iterations perform as well as the CG-CG inner-outer iterations in these tests. Second, we compare the CG methods using a two-grid preconditioning with fixed and randomly chosen coarse grids, and observe that the fixed preconditioner method is twice as slow as the method with random preconditioning.
Author Lashuk, Ilya
Knyazev, Andrew V.
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Cites_doi 10.1137/S0036142902401074
10.1137/S1064827502406415
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10.1007/BF02165472
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Issue 4
Keywords random preconditioning
Support
conjugate gradient
Steepest descent method
circular cone
Iterative method
Iteration
variable preconditioning
Multigrid
Convergence rate
Steepest descent
Real matrix
Conjugate gradient method
Cone
Grid pattern
Solving
convergence rate bound
Reflection
linear systems
multigrid; 65F10
Numerical analysis
Linear system
Symmetric matrix
Symmetric system
Linear algebra
Positive definite matrix
Condition number
Householder reflection
inner-outer iterations
preconditioner
Preconditioning
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Kantorovič L. V. (R7) 1947; 56
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Snippet We analyze the conjugate gradient (CG) method with variable preconditioning for solving a linear system with a real symmetric positive definite (SPD) matrix of...
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SubjectTerms Acceleration of convergence
Algebra
Algebraic geometry
Algorithms
Applied mathematics
Exact sciences and technology
Iterative methods
Linear and multilinear algebra, matrix theory
Mathematics
Methods
Numerical analysis
Numerical analysis. Scientific computation
Numerical linear algebra
Sciences and techniques of general use
Title Steepest Descent and Conjugate Gradient Methods with Variable Preconditioning
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