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Inner and Outer Product of 2 rank tensors


What does a zero tensor product imply?Is the tensor product of two torsion-free modules always non-zero?Universal Property of Tensor AlgebraTensor Product and Direct Sumcan quaternions be expressed in terms of tensor products?Product of Symmetric and Antisymmetric TensorsFunctor $R^2 otimes -$ for a ring $R$ is left-exact?Deduce that relation must hold for all unitary matricesTrace optimization of a function of a left stochastic matrixQuestion about creating a 3-rank tensor in numpy with python3













1












$begingroup$


I am trying to figure out whether or not the following identity is true:



$D_klA_ijA_kl=A_klD_klA_ij$



Or what I think is qually:



$D:(Aotimes A)= (A:D)A$



The matrices are both symmetric $A=A^T, B=B^T$.



I tried to "prove" it by simply doing the calculus with 2x2 matrices but I always end up wit another (wrong) result. I would very much appreciate it if you could help me or give me some hints whether this is right or wrong.










share|cite|improve this question









$endgroup$
















    1












    $begingroup$


    I am trying to figure out whether or not the following identity is true:



    $D_klA_ijA_kl=A_klD_klA_ij$



    Or what I think is qually:



    $D:(Aotimes A)= (A:D)A$



    The matrices are both symmetric $A=A^T, B=B^T$.



    I tried to "prove" it by simply doing the calculus with 2x2 matrices but I always end up wit another (wrong) result. I would very much appreciate it if you could help me or give me some hints whether this is right or wrong.










    share|cite|improve this question









    $endgroup$














      1












      1








      1





      $begingroup$


      I am trying to figure out whether or not the following identity is true:



      $D_klA_ijA_kl=A_klD_klA_ij$



      Or what I think is qually:



      $D:(Aotimes A)= (A:D)A$



      The matrices are both symmetric $A=A^T, B=B^T$.



      I tried to "prove" it by simply doing the calculus with 2x2 matrices but I always end up wit another (wrong) result. I would very much appreciate it if you could help me or give me some hints whether this is right or wrong.










      share|cite|improve this question









      $endgroup$




      I am trying to figure out whether or not the following identity is true:



      $D_klA_ijA_kl=A_klD_klA_ij$



      Or what I think is qually:



      $D:(Aotimes A)= (A:D)A$



      The matrices are both symmetric $A=A^T, B=B^T$.



      I tried to "prove" it by simply doing the calculus with 2x2 matrices but I always end up wit another (wrong) result. I would very much appreciate it if you could help me or give me some hints whether this is right or wrong.







      tensor-products matrix-calculus






      share|cite|improve this question













      share|cite|improve this question











      share|cite|improve this question




      share|cite|improve this question










      asked Mar 4 at 18:54









      Pablo JekenPablo Jeken

      1084




      1084




















          1 Answer
          1






          active

          oldest

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          1












          $begingroup$

          When employing index notation, you are effectively just summing over repeated indices, so if the resulting matrix is $M$, then



          $$ M_ij = sum_k=1^n sum_l=1^n D_klA_ijA_kl= sum_k=1^n sum_l=1^nA_klD_klA_ij = sum_k=1^n sum_l=1^n A_ijD_klA_kl= cdots
          $$



          The terms being multiplied inside the summation can be taken in any order.



          Thus, given definitions for "$otimes$" and "$:$" you can come up with different interpretations to an operation which is effectively just summing up the product of elements in two matrices/tensors in a certain order. All this provided the dimensions of the matrices allow for such an operation.






          share|cite|improve this answer








          New contributor




          Traws is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
          Check out our Code of Conduct.






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            1 Answer
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            active

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            active

            oldest

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            1












            $begingroup$

            When employing index notation, you are effectively just summing over repeated indices, so if the resulting matrix is $M$, then



            $$ M_ij = sum_k=1^n sum_l=1^n D_klA_ijA_kl= sum_k=1^n sum_l=1^nA_klD_klA_ij = sum_k=1^n sum_l=1^n A_ijD_klA_kl= cdots
            $$



            The terms being multiplied inside the summation can be taken in any order.



            Thus, given definitions for "$otimes$" and "$:$" you can come up with different interpretations to an operation which is effectively just summing up the product of elements in two matrices/tensors in a certain order. All this provided the dimensions of the matrices allow for such an operation.






            share|cite|improve this answer








            New contributor




            Traws is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
            Check out our Code of Conduct.






            $endgroup$

















              1












              $begingroup$

              When employing index notation, you are effectively just summing over repeated indices, so if the resulting matrix is $M$, then



              $$ M_ij = sum_k=1^n sum_l=1^n D_klA_ijA_kl= sum_k=1^n sum_l=1^nA_klD_klA_ij = sum_k=1^n sum_l=1^n A_ijD_klA_kl= cdots
              $$



              The terms being multiplied inside the summation can be taken in any order.



              Thus, given definitions for "$otimes$" and "$:$" you can come up with different interpretations to an operation which is effectively just summing up the product of elements in two matrices/tensors in a certain order. All this provided the dimensions of the matrices allow for such an operation.






              share|cite|improve this answer








              New contributor




              Traws is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
              Check out our Code of Conduct.






              $endgroup$















                1












                1








                1





                $begingroup$

                When employing index notation, you are effectively just summing over repeated indices, so if the resulting matrix is $M$, then



                $$ M_ij = sum_k=1^n sum_l=1^n D_klA_ijA_kl= sum_k=1^n sum_l=1^nA_klD_klA_ij = sum_k=1^n sum_l=1^n A_ijD_klA_kl= cdots
                $$



                The terms being multiplied inside the summation can be taken in any order.



                Thus, given definitions for "$otimes$" and "$:$" you can come up with different interpretations to an operation which is effectively just summing up the product of elements in two matrices/tensors in a certain order. All this provided the dimensions of the matrices allow for such an operation.






                share|cite|improve this answer








                New contributor




                Traws is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                Check out our Code of Conduct.






                $endgroup$



                When employing index notation, you are effectively just summing over repeated indices, so if the resulting matrix is $M$, then



                $$ M_ij = sum_k=1^n sum_l=1^n D_klA_ijA_kl= sum_k=1^n sum_l=1^nA_klD_klA_ij = sum_k=1^n sum_l=1^n A_ijD_klA_kl= cdots
                $$



                The terms being multiplied inside the summation can be taken in any order.



                Thus, given definitions for "$otimes$" and "$:$" you can come up with different interpretations to an operation which is effectively just summing up the product of elements in two matrices/tensors in a certain order. All this provided the dimensions of the matrices allow for such an operation.







                share|cite|improve this answer








                New contributor




                Traws is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                Check out our Code of Conduct.









                share|cite|improve this answer



                share|cite|improve this answer






                New contributor




                Traws is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                Check out our Code of Conduct.









                answered 2 days ago









                TrawsTraws

                6112




                6112




                New contributor




                Traws is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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                New contributor





                Traws is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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                Traws is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                Check out our Code of Conduct.



























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