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Methods for large scale total least squares problems. (English) Zbl 0974.65037
Authors’ abstract: The solution of the total least squares (TLS) problems, $\min_{E,f}\|(E, f)\|_F\quad\text{subject to }(A+E)x= b+f,$ can in the generic case be obtained from the right singular vector corresponding to the smallest singular value $$\sigma_{n+1}$$ of $$(A,b)$$. When $$A$$ is large and sparse (or structured) a method bases on Rayleigh quotient iteration (RQI) has been suggested by A. Björck [Proc. 2nd Int. Workshop on Total Least Squares, Leuven 1996, SIAM 149-160 (1997; Zbl 0879.65105)]. In this method the problem is reduced to the solution of a sequence of symmetric, positive definite linear systems of the form $$(A^TA- \overline\partial^2 I)z= g$$, where $$\overline\sigma$$ is an approximation to $$\sigma_{n+1}$$. These linear systems are then solved by a preconditioned conjugate gradient method (PCGTLS). For TLS problems where $$A$$ is large and sparse a (possibly incomplete) Cholesky factor of $$A^TA$$ can usually be computed, and this provides a very efficient preconditioner. The resulting method can be used to solve a much wider range of problems than it is possible to solve by using Lanczos-type algorithms directly for the singular value problem.
In this paper the RQI-PCGTLS methods are further developed, and the choice of initial approximation and termination criteria are discussed. Numerical results confirm that the given algorithm achieves rapid convergence and good accuracy.

##### MSC:
 65F20 Numerical solutions to overdetermined systems, pseudoinverses
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