Can a Hermitian Matrix be Decomposed into a Sum of Unitary Matricies?












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Given a Hermitian matrix $A$, when is it possible to write $A$ as a sum of unitary matricies as in the following form?



$$ A = sum_{i} a_i U$$



Where $U$ is unitary.



Intuitively, because you have a nice SVD: $A = U Sigma U^{dagger}$, I would expect to see that this is always possible with the coefficients somehow related to the eigenvalues, but I am not entirely sure.










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    0












    $begingroup$


    Given a Hermitian matrix $A$, when is it possible to write $A$ as a sum of unitary matricies as in the following form?



    $$ A = sum_{i} a_i U$$



    Where $U$ is unitary.



    Intuitively, because you have a nice SVD: $A = U Sigma U^{dagger}$, I would expect to see that this is always possible with the coefficients somehow related to the eigenvalues, but I am not entirely sure.










    share|cite|improve this question









    $endgroup$















      0












      0








      0





      $begingroup$


      Given a Hermitian matrix $A$, when is it possible to write $A$ as a sum of unitary matricies as in the following form?



      $$ A = sum_{i} a_i U$$



      Where $U$ is unitary.



      Intuitively, because you have a nice SVD: $A = U Sigma U^{dagger}$, I would expect to see that this is always possible with the coefficients somehow related to the eigenvalues, but I am not entirely sure.










      share|cite|improve this question









      $endgroup$




      Given a Hermitian matrix $A$, when is it possible to write $A$ as a sum of unitary matricies as in the following form?



      $$ A = sum_{i} a_i U$$



      Where $U$ is unitary.



      Intuitively, because you have a nice SVD: $A = U Sigma U^{dagger}$, I would expect to see that this is always possible with the coefficients somehow related to the eigenvalues, but I am not entirely sure.







      linear-algebra matrices






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      asked Apr 24 '16 at 3:21









      KF GaussKF Gauss

      1627




      1627






















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          $begingroup$

          I was too restrictive when I wrote this question and missed this result:
          Every matrix can be written as a sum of unitary matrices?
          Turns out every complex square matrix can be written as a linear sum of at most two unitary matricies.






          share|cite|improve this answer











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            1 Answer
            1






            active

            oldest

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            active

            oldest

            votes






            active

            oldest

            votes









            2












            $begingroup$

            I was too restrictive when I wrote this question and missed this result:
            Every matrix can be written as a sum of unitary matrices?
            Turns out every complex square matrix can be written as a linear sum of at most two unitary matricies.






            share|cite|improve this answer











            $endgroup$


















              2












              $begingroup$

              I was too restrictive when I wrote this question and missed this result:
              Every matrix can be written as a sum of unitary matrices?
              Turns out every complex square matrix can be written as a linear sum of at most two unitary matricies.






              share|cite|improve this answer











              $endgroup$
















                2












                2








                2





                $begingroup$

                I was too restrictive when I wrote this question and missed this result:
                Every matrix can be written as a sum of unitary matrices?
                Turns out every complex square matrix can be written as a linear sum of at most two unitary matricies.






                share|cite|improve this answer











                $endgroup$



                I was too restrictive when I wrote this question and missed this result:
                Every matrix can be written as a sum of unitary matrices?
                Turns out every complex square matrix can be written as a linear sum of at most two unitary matricies.







                share|cite|improve this answer














                share|cite|improve this answer



                share|cite|improve this answer








                edited Jan 28 at 0:26

























                answered Apr 24 '16 at 3:31









                KF GaussKF Gauss

                1627




                1627






























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