# SVD vs Eigenvalue Decompositon (Diagonalizability)

by eehsun
Tags: decompositon, diagonalizability, eigenvalue
 P: 9 Okay, I know that if I can't get n linearly independent eigenvectors out of a matrix A (∈ℝnxn), it is not diagonalizable (and that some necessary conditions for diagonalizability in this regard may be being symmetric and/or having distinct eigenvalues.) This is how things are for the usual eigenvalue decomposition (A=SΛS-1), right? However, if I am not mistaken, there is not such a restriction present on a matrix for being able to perform the SVD decomposition (A=UΣVT) on it. I mean, every matrix, irrespective of the state of its eigenvectors, can be decomposed into a three parts, one diagonal, two orthogonal, right? So doesn't this mean that every matrix is diagonizable, regardless of its eigenvectors? Thanks.. Edit: I know that the answer to the question is no but I don't understand why we don't consider Σ to be a diagonalized form of A. Please correct me whereever I am mistaken.. Thanks again.. :)
 P: 74 hi! U and V is different generally, so cannot be consider diagonalizable. Also, The diagonal entries of SVD is the square root of eigenvalue of A*A'(A'*A), so not the eigenvalue of A itself. They are the same iff A is normal.
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P: 38,881
 Quote by eehsun Okay, I know that if I can't get n linearly independent eigenvectors out of a matrix A (∈ℝnxn), it is not diagonalizable (and that some necessary conditions for diagonalizability in this regard may be being symmetric and/or having distinct eigenvalues.)
Those are sufficient conditions, not necessary conditions.

 This is how things are for the usual eigenvalue decomposition (A=SΛS-1), right? However, if I am not mistaken, there is not such a restriction present on a matrix for being able to perform the SVD decomposition (A=UΣVT) on it. I mean, every matrix, irrespective of the state of its eigenvectors, can be decomposed into a three parts, one diagonal, two orthogonal, right? So doesn't this mean that every matrix is diagonizable, regardless of its eigenvectors? Thanks.. Edit: I know that the answer to the question is no but I don't understand why we don't consider Σ to be a diagonalized form of A. Please correct me whereever I am mistaken.. Thanks again.. :)

P: 74

## SVD vs Eigenvalue Decompositon (Diagonalizability)

 Quote by td21 hi! U and V is different generally, so cannot be consider diagonalizable. Also, The diagonal entries of SVD is the square root of eigenvalue of A*A'(A'*A), so not the eigenvalue of A itself. They are the same iff A is normal.
sorry... should be positive semidefinite.

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