Nicholas J. Higham

Functions of Matrices: Theory and Computation

A thorough and elegant treatment of the theory of matrix functions and numerical methods for computing them, including an overview of applications, new and unpublished research results, and improved algorithms. Key features include a detailed treatment of the matrix sign function and matrix roots; a development of the theory of conditioning and properties of the Frechet derivative; Schur decomposition; block Parlett recurrence; a thorough analysis of the accuracy, stability, and computational cost of numerical methods; general results on convergence and stability of matrix iterations; and a chapter devoted to the f(A)b problem. Ideal for advanced courses and for self-study, its broad content, references and appendix also make this book a convenient general reference. Contains an extensive collection of problems with solutions and MATLAB implementations of key algorithms.

Computing a nearest symmetric positive semidefinite matrix

The nearest symmetric positive semidefinite matrix in the Frobenius norm to an arbitrary real matrix A is shown to be (B + H)/2, where H is the symmetric polar factor of B=(A + AT)/2. In the 2-norm a nearest symmetric positive semidefinite matrix, and its distance δ2(A) from A, are given by a computationally challenging formula due to Halmos. We show how the bisection method can be applied to this formula to compute upper and lower bounds for δ2(A) differing by no more than a given amount. A key ingredient is a stable and efficient test for positive definiteness, based on an attempted Choleski decomposition. For accurate computation of δ2(A) we formulate the problem as one of zero finding and apply a hybrid Newton-bisection algorithm. Some numerical difficulties are discussed and illustrated by example.

Computing the polar decomposition with applications

A quadratically convergent Newton method for computing the polar decomposition of a full-rank matrix is presented and analysed. Acceleration parameters are introduced so as to enhance the initial rate of convergence and it is shown how reliable estimates of the optimal parameters may be computed in practice.To add to the known best approximation property of the unitary polar factor, the Hermitian polar factor H of a nonsingular Hermitian matrix A is shown to be a good positive definite approximation to Aand

Computing the Action of the Matrix Exponential, with an Application to Exponential Integrators

\frac{1}{2}(A + H)

The accuracy of floating point summation

is shown to be a best Hermitian positive semi-definite approximation to A. Perturbation bounds for the polar factors are derived.Applications of the polar decomposition to factor analysis, aerospace computations and optimisation are outlined; and a new method is derived for computing the square root of a symmetric positive definite matrix.

Computing real square roots of a real matrix

A new algorithm is developed for computing

FORTRAN codes for estimating the one-norm of a real or complex matrix, with applications to condition estimation

e^{tA}B

NLEVP: A Collection of Nonlinear Eigenvalue Problems

, where

Structured Pseudospectra for Polynomial Eigenvalue Problems, with Applications

A

Stable iterations for the matrix square root

is an