Orthogonal transformation of matrix

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SUMMARY

The discussion focuses on the properties of the 2-norm in relation to orthogonal transformations of matrices, specifically addressing the equation || Q^H*A*Q ||2 = || A ||2 for an orthogonal matrix Q. It is established that the 2-norm remains invariant under orthogonal transformations, as long as Q satisfies the condition Q^T*Q=I. The conversation emphasizes the need to verify whether the transformation (Q^H*A*Q)^HQ^H*A*Q maintains the absolute eigenvalues of A^HA, which is crucial for proving the invariance of the 2-norm.

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  • Understanding of matrix norms, specifically the 2-norm.
  • Familiarity with orthogonal matrices and their properties.
  • Knowledge of eigenvalues and eigenvectors in linear algebra.
  • Experience with complex conjugate transposes (Q^H) in matrix operations.
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  • Study the properties of orthogonal matrices in linear algebra.
  • Learn about the spectral theorem and its implications for eigenvalues.
  • Explore the concept of matrix norms in greater depth, focusing on the 2-norm.
  • Investigate the relationship between matrix transformations and eigenvalue preservation.
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vabamyyr
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I have a question on matrix norms and orthogonal transformations. The 2-norm in invariant under orthogonal transformation, for if Q^T*Q=I. But i have trouble showing that for orthogonal Q and Q^H with appropriate dimensions

|| Q^H*A*Q ||2 =|| A ||2
 
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The 2-norm of A returns the square-root of the maximum absolute eigenvalues of A^HA. So check, does (Q^HA*Q)^HQ^HA*Q preserve the absolute eigenvalues of A^HA?
 

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