References$(function(){PrimeFaces.cw("TieredMenu","widget_formSmash_upper_j_idt145",{id:"formSmash:upper:j_idt145",widgetVar:"widget_formSmash_upper_j_idt145",autoDisplay:true,overlay:true,my:"left top",at:"left bottom",trigger:"formSmash:upper:referencesLink",triggerEvent:"click"});}); $(function(){PrimeFaces.cw("OverlayPanel","widget_formSmash_upper_j_idt146_j_idt148",{id:"formSmash:upper:j_idt146:j_idt148",widgetVar:"widget_formSmash_upper_j_idt146_j_idt148",target:"formSmash:upper:j_idt146:permLink",showEffect:"blind",hideEffect:"fade",my:"right top",at:"right bottom",showCloseIcon:true});});

Computing all pairs (lambda,mu) such that lambdais a double eigenvalue of A plus mu BPrimeFaces.cw("AccordionPanel","widget_formSmash_some",{id:"formSmash:some",widgetVar:"widget_formSmash_some",multiple:true}); PrimeFaces.cw("AccordionPanel","widget_formSmash_all",{id:"formSmash:all",widgetVar:"widget_formSmash_all",multiple:true});
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PrimeFaces.cw("AccordionPanel","widget_formSmash_responsibleOrgs",{id:"formSmash:responsibleOrgs",widgetVar:"widget_formSmash_responsibleOrgs",multiple:true}); 2011 (English)In: SIAM Journal on Matrix Analysis and Applications, ISSN 0895-4798, E-ISSN 1095-7162, Vol. 32, no 3, 902-927 p.Article in journal (Refereed) Published
##### Abstract [en]

##### Place, publisher, year, edition, pages

2011. Vol. 32, no 3, 902-927 p.
##### Keyword [en]

ANALYTIC MATRIX FUNCTIONS; HOLDER CONDITION NUMBERS; MULTIPLE-EIGENVALUES; PERTURBATION-THEORY; PSEUDOSPECTRA; COMPUTATION; STABILITY; FORMULA; SYSTEMS
##### National Category

Computer and Information Science
##### Identifiers

URN: urn:nbn:se:kth:diva-53361DOI: 10.1137/100783157ISI: 000295399200012ScopusID: 2-s2.0-80054044730OAI: oai:DiVA.org:kth-53361DiVA: diva2:469989
#####

PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt375",{id:"formSmash:j_idt375",widgetVar:"widget_formSmash_j_idt375",multiple:true});
#####

PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt381",{id:"formSmash:j_idt381",widgetVar:"widget_formSmash_j_idt381",multiple:true});
#####

PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt387",{id:"formSmash:j_idt387",widgetVar:"widget_formSmash_j_idt387",multiple:true});
##### Note

QC 20120207Available from: 2011-12-27 Created: 2011-12-27 Last updated: 2012-02-07Bibliographically approved

Double eigenvalues are not generic for matrices without any particular structure. A matrix depending linearly on a scalar parameter, A + mu B, will, however, generically have double eigenvalues for some values of the parameter mu. In this paper, we consider the problem of finding those values. More precisely, we construct a method to accurately find all scalar pairs (lambda, mu) such that A + mu B has a double eigenvalue lambda, where A and B are given arbitrary complex matrices. The general idea of the globally convergent method is that if mu is close to a solution, then A + mu B has two eigenvalues which are close to each other. We fix the relative distance between these two eigenvalues and construct a method to solve and study it by observing that the resulting problem can be stated as a two-parameter eigenvalue problem, which is already studied in the literature. The method, which we call the method of fixed relative distance (MFRD), involves solving a two-parameter eigenvalue problem which returns approximations of all solutions. It is unfortunately not possible to get full accuracy with MFRD. In order to compute solutions with full accuracy, we present an iterative method which returns a very accurate solution, for a sufficiently good starting value. The approach is illustrated with one academic example and one application to a simple problem in computational quantum mechanics.

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