Hermitian Adjoint Article Index for
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Hermitian Adjoint




Adjoints of operators generalize Conjugate Transpose s of square matrices to (possibly) infinite-dimensional situations. If one thinks of operators on a Hilbert space as "generalized complex numbers", then the adjoint of an operator plays the role of the Complex Conjugate of a complex number.

  • or ''A'' (the latter especially when used in conjunction with the Bra-ket Notation ).



DEFINITION FOR BOUNDED OPERATORS


Suppose ''H'' is a ).

Using the Riesz Representation Theorem , one can show that there exists a unique continuous linear operator
  • '' : ''H'' → ''H'' with the following property:


  • y ang \quad \mbox{for all } x,y\in H


  • is the adjoint of ''A''.



PROPERTIES


Immediate properties:
  • --- = ''A''

  • . Then, (''A''---)−1 = (''A''−1)---

  • = ''A''--- + ''B''---

  • = λ--- ''A''---, where λ--- denotes the Complex Conjugate of the Complex Number λ

  • = ''B''--- ''A''---


If we define the Operator Norm of ''A'' by
  :<math> \ A^ \ {op} \ A \ _{op} </math>
  :<math> \ A^ A \ {op} \ A \ _{op}^2 </math>