Linear algebra - eigenvalues and eigenvectors and hermitian

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Homework Help Overview

The discussion revolves around a linear algebra problem concerning eigenvalues and eigenvectors of a Hermitian matrix. The original poster presents their calculations for the eigenvalues and corresponding eigenvectors, along with an attempt to reconstruct the original matrix using these components.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to calculate the eigenvalues and eigenvectors, but expresses confusion regarding the reconstruction of the original matrix from these components. Some participants question the completeness of the provided information, specifically the absence of a visual representation of the problem.

Discussion Status

The discussion has progressed with the original poster receiving guidance on normalizing their eigenvectors, which appears to have resolved their confusion regarding the reconstruction of the matrix. There is an acknowledgment of the need for further clarification on the spectral decomposition concept.

Contextual Notes

There was an initial lack of visual context due to a missing attachment, which was later provided. The original poster's calculations and assumptions are under scrutiny, particularly regarding the normalization of eigenvectors.

SpiffyEh
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Homework Statement



I attached the problem in a picture so its easier to see.

Homework Equations





The Attempt at a Solution



These are the values i got
[tex]\lambda[/tex]_ 1 = 1
[tex]\lambda[/tex]_ 2 = -1

x_1 = [-i; 1] (x_1)^H = [i 1]
x_2 = [ i; 1] (x_2)^H = [-i 1]
* where x_1 and x_2 are 2x1 matricies, and their hermitians are 1x2

after each multiplication I got
[tex]\lambda[/tex]_ 1 x_1 (x_1)^H =
[1 -i
i 1]

[tex]\lambda[/tex]_ 2 x_2 (x_2)^H =
[-1 -i
i -1]

When I add these together I get
[0 -2i
2i 0]

which is not the original A_5. I can't figure out where I went wrong in this process. If someone could look over it and let me know that would be great. Thank you
 

Attachments

  • problem.png
    problem.png
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Last edited:
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No picture?
 
Did you forget the picture, I can't see any.
 
I think I forgot to press the upload button after trying to attach it. Sorry about that. I edited it and it's there now
 
The spectral decomposition allows you to write a Hermitian matrix as a linear combination of projections onto the orthonormal basis of eigenvectors. So you need to normalize your eigenvectors, and then the 2 will nicely vanish.
 
oh! that worked perfectly. Thank you, I would've never gotten that
 

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