CaltechTHESIS
A Caltech Library Service

# On the Lyapunov Transformation for Stable Matrices

## Citation

Loewy, Raphael (1972) On the Lyapunov Transformation for Stable Matrices. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/EXGT-0968. https://resolver.caltech.edu/CaltechTHESIS:05092016-130648083

## Abstract

The matrices studied here are positive stable (or briefly stable). These are matrices, real or complex, whose eigenvalues have positive real parts. A theorem of Lyapunov states that A is stable if and only if there exists H ˃ 0 such that AH + HA* = I. Let A be a stable matrix. Three aspects of the Lyapunov transformation LA :H → AH + HA* are discussed.

1. Let C1 (A) = {AH + HA* :H ≥ 0} and C2 (A) = {H: AH+HA* ≥ 0}. The problems of determining the cones C1(A) and C2(A) are still unsolved. Using solvability theory for linear equations over cones it is proved that C1(A) is the polar of C2(A*), and it is also shown that C1 (A) = C1(A-1). The inertia assumed by matrices in C1(A) is characterized.

2. The index of dissipation of A was defined to be the maximum number of equal eigenvalues of H, where H runs through all matrices in the interior of C2(A). Upper and lower bounds, as well as some properties of this index, are given.

3. We consider the minimal eigenvalue of the Lyapunov transform AH+HA*, where H varies over the set of all positive semi-definite matrices whose largest eigenvalue is less than or equal to one. Denote it by ψ(A). It is proved that if A is Hermitian and has eigenvalues μ1 ≥ μ2…≥ μn ˃ 0, then ψ(A) = -(μ1n)2/(4(μ1 + μn)). The value of ψ(A) is also determined in case A is a normal, stable matrix. Then ψ(A) can be expressed in terms of at most three of the eigenvalues of A. If A is an arbitrary stable matrix, then upper and lower bounds for ψ(A) are obtained.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:(Mathematics)
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Mathematics
Thesis Availability:Public (worldwide access)
• Taussky-Todd, Olga
Thesis Committee:
• Unknown, Unknown
Defense Date:8 March 1972
Funders:
Funding AgencyGrant Number
CaltechUNSPECIFIED
Ford FoundationUNSPECIFIED
Record Number:CaltechTHESIS:05092016-130648083
Persistent URL:https://resolver.caltech.edu/CaltechTHESIS:05092016-130648083
DOI:10.7907/EXGT-0968
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:9710
Collection:CaltechTHESIS
Deposited By:INVALID USER
Deposited On:09 May 2016 22:20