How to use QR decomposition to find eigenvalues?

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SUMMARY

The discussion focuses on utilizing QR decomposition to compute the eigenvalues of a matrix. The key equation presented is A = QR, where Q is an orthogonal matrix satisfying QT = Q-1. The iterative nature of the QR algorithm is emphasized, indicating that the eigenvalues obtained through this method are approximations rather than exact values. A reference link to a detailed resource on QR decomposition is also provided for further reading.

PREREQUISITES
  • Understanding of matrix factorization, specifically QR decomposition.
  • Familiarity with eigenvalues and eigenvectors in linear algebra.
  • Knowledge of orthogonal matrices and their properties.
  • Basic proficiency in determinants and their role in eigenvalue calculations.
NEXT STEPS
  • Study the iterative QR algorithm for eigenvalue approximation.
  • Learn about the convergence properties of the QR method.
  • Explore the relationship between QR decomposition and other eigenvalue algorithms, such as the Jacobi method.
  • Review practical applications of eigenvalues in data analysis and machine learning.
USEFUL FOR

Students and professionals in mathematics, engineering, and computer science who are looking to deepen their understanding of eigenvalue computation methods, particularly those interested in numerical linear algebra.

Hercuflea
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Homework Statement


I need to understand how I would go about using QR decomposition of a matrix to find the matrix's eigenvalues. I know how to find the factorization, just stuck on how I would use that factorization to find the eigenvalues.


Homework Equations



A=QR where Q is an orthogonal matrix such that Qtranspose = Qinverse

The Attempt at a Solution



det(λ*I - QR) = 0? this doesn't really help.
 
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If you do a google search, you will find a number of different hits on this topic.

Here is one such hit: http://www.mcs.csueastbay.edu/~malek/TeX/Qr.pdf

The use of QR for finding eigenvalues is iterative, however. The values returned are approximations of the true eigenvalues.
 

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