Diagonal Linear Operator T in L(H): Examples

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SUMMARY

The discussion focuses on diagonal linear operators T in the context of L(H), where H represents a Hilbert space. A key example provided is the identity operator I, which is diagonalizable, bounded, and not compact. The distinction between diagonal and diagonalizable operators is emphasized, as the latter depends on the chosen orthonormal basis. The user seeks examples of diagonal operators that are bounded but not compact, as well as compact operators that are not Hilbert-Schmidt.

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Mikemaths
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I am trying to find an example of a diagonal linear operator T in L(H) H is hilbert space that is bounded but not compact and also one which is compact but not Hilbert-Schmidt. any Ideas??

Where diagonal means Ten=§en where § is the eigenvalue and en is on orthonormal basis.
 
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(Instead of diagonal, I would say diagonalizable, since it depends on the chosen basis so is not an intrinsic property of the operator.)

The identity operator I is diagonalizable (well, I is of course diagonal w.r.t. every basis), bounded, but not compact.
 

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