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## 2.1 Chebyshev Semi-Iterative Method

The error vector for the iterate from Equation (3), , can be written as

From the theory of summability of sequences [23], consider the more general iterative procedure

The requirement that if , then must be x, results in the constraint

The iterative method resulting from the sequence will be referred to as a semi-iterative method [23] and the error vector corresponding to is given by the expression

where is an degree polynomial with and .

In order to accelerate the convergence of the semi-iterative method, it is necessary to minimize the average rate of convergence, or, equivalently, obtain the solution of the minimization problem

The solution of this problem requires a priori determination of the eigenvalues. In its place, consider the new minimization problem

where . The solution of the new minimization problem is given in terms of the Chebyshev polynomials, , defined by

for

Using the 3-term recurrence for Chebyshev polynomials

and the fact that , one can generate an iteration of the form (see [23])

where and . This iterative procedure specifies the Chebyshev semi-iterative method with respect to the original iteration defined in Equation (3). Discussions of the convergence of this method are presented in [13] and [22].

As shown in [10], the iteration defined by Equation (10) can be used in combination with the theory of modified moments to produce approximations to the largest eigenvalues of the matrix M. Specifically, Equation (10) may be used to generate iterates through the iteration

Similar to the Lanczos algorithm (see [5] and [11]) the next section will show how modified moments derived from the iterates may be used to generate a sequence of bidiagonal matrices whose largest singular values approximate those of the sparse matrix A.

Next: Modified Moments and Up: Derivation of CSI-MSVD Previous: Derivation of CSI-MSVD

Michael W. Berry (berry@cs.utk.edu)
Sun May 19 11:34:27 EDT 1996