Guo, ChunHua and Higham, Nicholas J. (2006) A SchurNewton Method for the Matrix p'th Root and its Inverse. SIAM Journal On Matrix Analysis and Applications, 28 (3). pp. 788804. ISSN 08954798
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Abstract
Newton's method for the inverse matrix $p$th root, $A^{1/p}$, has the attraction that it involves only matrix multiplication. We show that if the starting matrix is $c^{1}I$ for $c\in\R^+$ then the iteration converges quadratically to $A^{1/p}$ if the eigenvalues of $A$ lie in a wedgeshaped convex set containing the disc $\{\, z: zc^p < c^p\,\}$. We derive an optimal choice of $c$ for the case where $A$ has real, positive eigenvalues. An application is described to roots of transition matrices from Markov models, in which for certain problems the convergence condition is satisfied with $c=1$. Although the basic Newton iteration is numerically unstable, a coupled version is stable and a simple modification of it provides a new coupled iteration for the matrix $p$th root. For general matrices we develop a hybrid algorithm that computes a Schur decomposition, takes square roots of the upper (quasi)triangular factor, and applies the coupled Newton iteration to a matrix for which fast convergence is guaranteed. The new algorithm can be used to compute either $A^{1/p}$ or $A^{1/p}$, and for large $p$ that are not highly composite it is more efficient than the method of Smith based entirely on the Schur decomposition.
Item Type:  Article 

Uncontrolled Keywords:  Matrix $p$th root, principal $p$th root, matrix logarithm, inverse, Newton's method, preprocessing, Schur decomposition, numerical stability, convergence, Markov model, transition matrix 
Subjects:  MSC 2010, the AMS's Mathematics Subject Classification > 15 Linear and multilinear algebra; matrix theory MSC 2010, the AMS's Mathematics Subject Classification > 65 Numerical analysis 
Depositing User:  Nick Higham 
Date Deposited:  09 Oct 2006 
Last Modified:  20 Oct 2017 14:12 
URI:  http://eprints.maths.manchester.ac.uk/id/eprint/623 
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A SchurNewton Method for the Matrix p'th Root and its Inverse. (deposited 16 Feb 2006)
 A SchurNewton Method for the Matrix p'th Root and its Inverse. (deposited 09 Oct 2006) [Currently Displayed]
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