Tensor equation [closed]












1












$begingroup$


If you have two antisymmetric tensors $A_{mu nu}$ and $B_{mu nu}$, and for every anti symmetric tensor $epsilon^{mu nu}$,



$epsilon^{mu nu} A_{mu nu} = epsilon^{mu nu} B_{mu nu}$



Is it true that



$A_{mu nu} = B_{mu nu}$ ?



Summation over the indices is assumed.










share|cite|improve this question











$endgroup$



closed as off-topic by Eevee Trainer, Adrian Keister, Lee David Chung Lin, A. Pongrácz, Namaste Jan 14 at 18:23


This question appears to be off-topic. The users who voted to close gave this specific reason:


  • "This question is missing context or other details: Please provide additional context, which ideally explains why the question is relevant to you and our community. Some forms of context include: background and motivation, relevant definitions, source, possible strategies, your current progress, why the question is interesting or important, etc." – Eevee Trainer, Adrian Keister, Lee David Chung Lin, A. Pongrácz, Namaste

If this question can be reworded to fit the rules in the help center, please edit the question.
















  • $begingroup$
    What is $epsilon^{munu}$ ?
    $endgroup$
    – Sou
    Jan 14 at 8:39












  • $begingroup$
    It's just a general tensor. But I changed the question now, supposing it is anti symmetric.
    $endgroup$
    – Higgsino
    Jan 14 at 8:44
















1












$begingroup$


If you have two antisymmetric tensors $A_{mu nu}$ and $B_{mu nu}$, and for every anti symmetric tensor $epsilon^{mu nu}$,



$epsilon^{mu nu} A_{mu nu} = epsilon^{mu nu} B_{mu nu}$



Is it true that



$A_{mu nu} = B_{mu nu}$ ?



Summation over the indices is assumed.










share|cite|improve this question











$endgroup$



closed as off-topic by Eevee Trainer, Adrian Keister, Lee David Chung Lin, A. Pongrácz, Namaste Jan 14 at 18:23


This question appears to be off-topic. The users who voted to close gave this specific reason:


  • "This question is missing context or other details: Please provide additional context, which ideally explains why the question is relevant to you and our community. Some forms of context include: background and motivation, relevant definitions, source, possible strategies, your current progress, why the question is interesting or important, etc." – Eevee Trainer, Adrian Keister, Lee David Chung Lin, A. Pongrácz, Namaste

If this question can be reworded to fit the rules in the help center, please edit the question.
















  • $begingroup$
    What is $epsilon^{munu}$ ?
    $endgroup$
    – Sou
    Jan 14 at 8:39












  • $begingroup$
    It's just a general tensor. But I changed the question now, supposing it is anti symmetric.
    $endgroup$
    – Higgsino
    Jan 14 at 8:44














1












1








1


1



$begingroup$


If you have two antisymmetric tensors $A_{mu nu}$ and $B_{mu nu}$, and for every anti symmetric tensor $epsilon^{mu nu}$,



$epsilon^{mu nu} A_{mu nu} = epsilon^{mu nu} B_{mu nu}$



Is it true that



$A_{mu nu} = B_{mu nu}$ ?



Summation over the indices is assumed.










share|cite|improve this question











$endgroup$




If you have two antisymmetric tensors $A_{mu nu}$ and $B_{mu nu}$, and for every anti symmetric tensor $epsilon^{mu nu}$,



$epsilon^{mu nu} A_{mu nu} = epsilon^{mu nu} B_{mu nu}$



Is it true that



$A_{mu nu} = B_{mu nu}$ ?



Summation over the indices is assumed.







matrices mathematical-physics tensors index-notation






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Jan 14 at 13:44









Sou

3,2892923




3,2892923










asked Jan 14 at 8:27









HiggsinoHiggsino

595




595




closed as off-topic by Eevee Trainer, Adrian Keister, Lee David Chung Lin, A. Pongrácz, Namaste Jan 14 at 18:23


This question appears to be off-topic. The users who voted to close gave this specific reason:


  • "This question is missing context or other details: Please provide additional context, which ideally explains why the question is relevant to you and our community. Some forms of context include: background and motivation, relevant definitions, source, possible strategies, your current progress, why the question is interesting or important, etc." – Eevee Trainer, Adrian Keister, Lee David Chung Lin, A. Pongrácz, Namaste

If this question can be reworded to fit the rules in the help center, please edit the question.







closed as off-topic by Eevee Trainer, Adrian Keister, Lee David Chung Lin, A. Pongrácz, Namaste Jan 14 at 18:23


This question appears to be off-topic. The users who voted to close gave this specific reason:


  • "This question is missing context or other details: Please provide additional context, which ideally explains why the question is relevant to you and our community. Some forms of context include: background and motivation, relevant definitions, source, possible strategies, your current progress, why the question is interesting or important, etc." – Eevee Trainer, Adrian Keister, Lee David Chung Lin, A. Pongrácz, Namaste

If this question can be reworded to fit the rules in the help center, please edit the question.












  • $begingroup$
    What is $epsilon^{munu}$ ?
    $endgroup$
    – Sou
    Jan 14 at 8:39












  • $begingroup$
    It's just a general tensor. But I changed the question now, supposing it is anti symmetric.
    $endgroup$
    – Higgsino
    Jan 14 at 8:44


















  • $begingroup$
    What is $epsilon^{munu}$ ?
    $endgroup$
    – Sou
    Jan 14 at 8:39












  • $begingroup$
    It's just a general tensor. But I changed the question now, supposing it is anti symmetric.
    $endgroup$
    – Higgsino
    Jan 14 at 8:44
















$begingroup$
What is $epsilon^{munu}$ ?
$endgroup$
– Sou
Jan 14 at 8:39






$begingroup$
What is $epsilon^{munu}$ ?
$endgroup$
– Sou
Jan 14 at 8:39














$begingroup$
It's just a general tensor. But I changed the question now, supposing it is anti symmetric.
$endgroup$
– Higgsino
Jan 14 at 8:44




$begingroup$
It's just a general tensor. But I changed the question now, supposing it is anti symmetric.
$endgroup$
– Higgsino
Jan 14 at 8:44










3 Answers
3






active

oldest

votes


















1












$begingroup$

For $n=2$, this is true. For the equality is
$$
epsilon^{12}A_{12}+epsilon^{21}A_{21} = epsilon^{12}B_{12}+epsilon^{21}B_{21} implies 2epsilon^{12}A_{12} = 2epsilon^{12}B_{12}.
$$

So $B_{12}=A_{12}$ and $A_{21}=-A_{12} = -B_{12} = B_{21}$ and $A_{ii}=B_{ii} = 0$ for all $i$. For $ngeq3$ this is false generally. The counterexample is
$$
[epsilon^{ij}] = begin{pmatrix} 0 & 1 & 1\ -1 & 0 & 1 \ -1 & -1 & 0 end{pmatrix},
[A_{ij}] = begin{pmatrix} 0 & 0 & 1\ 0 & 0 & 0 \ -1 & 0 & 0 end{pmatrix},
[B_{ij}] = begin{pmatrix} 0 & 1/3 & 1/3\ -1/3 & 0 & 1/3 \ -1/3 & -1/3 & 0 end{pmatrix}.
$$






share|cite|improve this answer









$endgroup$













  • $begingroup$
    Wow, nice! Tensors :P !!!
    $endgroup$
    – user2662833
    Jan 14 at 11:42










  • $begingroup$
    I just double checked your counter example, I don't believe $e^{ij} A_{ij} = e^{ij} B_{ij}$ In this example. have I made a mistake?
    $endgroup$
    – user2662833
    Jan 14 at 11:48










  • $begingroup$
    @user2662833 Just compute lhs and rhs separately by using the antisymmetry property (or not, whatever). E.g. lhs is $epsilon^{12}A_{12}+epsilon^{13}A_{13}+epsilon^{21}A_{21}+epsilon^{23}A_{23}+epsilon^{31}A_{31}+epsilon^{32}A_{32} = 2epsilon^{12}A_{12}+2epsilon^{13}A_{13}+2epsilon^{23}A_{23}=2$
    $endgroup$
    – Sou
    Jan 14 at 13:22



















0












$begingroup$

Reason I asked is because of this example found from the book "A first course in string theory".



enter image description here



I don't understand the step when he cancels $epsilon$ on both sides because the dimension is generally bigger then 2 I think.






share|cite|improve this answer











$endgroup$













  • $begingroup$
    Here we must be careful that 8.55 follows from 8.22 which is a definition not an equality. So here we actually want to know what is the current looks like if we have such a Langrangian.
    $endgroup$
    – Sou
    Jan 14 at 14:01










  • $begingroup$
    I suppose the reason we can cancel $epsilon$ on both sides is because it consists of different parameters which are independent of each other. So we can vary one parameter on both sides keeping the other parameters constant. And therefore we can match terms even if we have a sum of terms on both sides. It's like the separation of variable method when solving partial differential equations.
    $endgroup$
    – Higgsino
    Jan 14 at 14:19



















0












$begingroup$

8.22) which you asked for is the following relation.



enter image description here






share|cite|improve this answer









$endgroup$




















    3 Answers
    3






    active

    oldest

    votes








    3 Answers
    3






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    1












    $begingroup$

    For $n=2$, this is true. For the equality is
    $$
    epsilon^{12}A_{12}+epsilon^{21}A_{21} = epsilon^{12}B_{12}+epsilon^{21}B_{21} implies 2epsilon^{12}A_{12} = 2epsilon^{12}B_{12}.
    $$

    So $B_{12}=A_{12}$ and $A_{21}=-A_{12} = -B_{12} = B_{21}$ and $A_{ii}=B_{ii} = 0$ for all $i$. For $ngeq3$ this is false generally. The counterexample is
    $$
    [epsilon^{ij}] = begin{pmatrix} 0 & 1 & 1\ -1 & 0 & 1 \ -1 & -1 & 0 end{pmatrix},
    [A_{ij}] = begin{pmatrix} 0 & 0 & 1\ 0 & 0 & 0 \ -1 & 0 & 0 end{pmatrix},
    [B_{ij}] = begin{pmatrix} 0 & 1/3 & 1/3\ -1/3 & 0 & 1/3 \ -1/3 & -1/3 & 0 end{pmatrix}.
    $$






    share|cite|improve this answer









    $endgroup$













    • $begingroup$
      Wow, nice! Tensors :P !!!
      $endgroup$
      – user2662833
      Jan 14 at 11:42










    • $begingroup$
      I just double checked your counter example, I don't believe $e^{ij} A_{ij} = e^{ij} B_{ij}$ In this example. have I made a mistake?
      $endgroup$
      – user2662833
      Jan 14 at 11:48










    • $begingroup$
      @user2662833 Just compute lhs and rhs separately by using the antisymmetry property (or not, whatever). E.g. lhs is $epsilon^{12}A_{12}+epsilon^{13}A_{13}+epsilon^{21}A_{21}+epsilon^{23}A_{23}+epsilon^{31}A_{31}+epsilon^{32}A_{32} = 2epsilon^{12}A_{12}+2epsilon^{13}A_{13}+2epsilon^{23}A_{23}=2$
      $endgroup$
      – Sou
      Jan 14 at 13:22
















    1












    $begingroup$

    For $n=2$, this is true. For the equality is
    $$
    epsilon^{12}A_{12}+epsilon^{21}A_{21} = epsilon^{12}B_{12}+epsilon^{21}B_{21} implies 2epsilon^{12}A_{12} = 2epsilon^{12}B_{12}.
    $$

    So $B_{12}=A_{12}$ and $A_{21}=-A_{12} = -B_{12} = B_{21}$ and $A_{ii}=B_{ii} = 0$ for all $i$. For $ngeq3$ this is false generally. The counterexample is
    $$
    [epsilon^{ij}] = begin{pmatrix} 0 & 1 & 1\ -1 & 0 & 1 \ -1 & -1 & 0 end{pmatrix},
    [A_{ij}] = begin{pmatrix} 0 & 0 & 1\ 0 & 0 & 0 \ -1 & 0 & 0 end{pmatrix},
    [B_{ij}] = begin{pmatrix} 0 & 1/3 & 1/3\ -1/3 & 0 & 1/3 \ -1/3 & -1/3 & 0 end{pmatrix}.
    $$






    share|cite|improve this answer









    $endgroup$













    • $begingroup$
      Wow, nice! Tensors :P !!!
      $endgroup$
      – user2662833
      Jan 14 at 11:42










    • $begingroup$
      I just double checked your counter example, I don't believe $e^{ij} A_{ij} = e^{ij} B_{ij}$ In this example. have I made a mistake?
      $endgroup$
      – user2662833
      Jan 14 at 11:48










    • $begingroup$
      @user2662833 Just compute lhs and rhs separately by using the antisymmetry property (or not, whatever). E.g. lhs is $epsilon^{12}A_{12}+epsilon^{13}A_{13}+epsilon^{21}A_{21}+epsilon^{23}A_{23}+epsilon^{31}A_{31}+epsilon^{32}A_{32} = 2epsilon^{12}A_{12}+2epsilon^{13}A_{13}+2epsilon^{23}A_{23}=2$
      $endgroup$
      – Sou
      Jan 14 at 13:22














    1












    1








    1





    $begingroup$

    For $n=2$, this is true. For the equality is
    $$
    epsilon^{12}A_{12}+epsilon^{21}A_{21} = epsilon^{12}B_{12}+epsilon^{21}B_{21} implies 2epsilon^{12}A_{12} = 2epsilon^{12}B_{12}.
    $$

    So $B_{12}=A_{12}$ and $A_{21}=-A_{12} = -B_{12} = B_{21}$ and $A_{ii}=B_{ii} = 0$ for all $i$. For $ngeq3$ this is false generally. The counterexample is
    $$
    [epsilon^{ij}] = begin{pmatrix} 0 & 1 & 1\ -1 & 0 & 1 \ -1 & -1 & 0 end{pmatrix},
    [A_{ij}] = begin{pmatrix} 0 & 0 & 1\ 0 & 0 & 0 \ -1 & 0 & 0 end{pmatrix},
    [B_{ij}] = begin{pmatrix} 0 & 1/3 & 1/3\ -1/3 & 0 & 1/3 \ -1/3 & -1/3 & 0 end{pmatrix}.
    $$






    share|cite|improve this answer









    $endgroup$



    For $n=2$, this is true. For the equality is
    $$
    epsilon^{12}A_{12}+epsilon^{21}A_{21} = epsilon^{12}B_{12}+epsilon^{21}B_{21} implies 2epsilon^{12}A_{12} = 2epsilon^{12}B_{12}.
    $$

    So $B_{12}=A_{12}$ and $A_{21}=-A_{12} = -B_{12} = B_{21}$ and $A_{ii}=B_{ii} = 0$ for all $i$. For $ngeq3$ this is false generally. The counterexample is
    $$
    [epsilon^{ij}] = begin{pmatrix} 0 & 1 & 1\ -1 & 0 & 1 \ -1 & -1 & 0 end{pmatrix},
    [A_{ij}] = begin{pmatrix} 0 & 0 & 1\ 0 & 0 & 0 \ -1 & 0 & 0 end{pmatrix},
    [B_{ij}] = begin{pmatrix} 0 & 1/3 & 1/3\ -1/3 & 0 & 1/3 \ -1/3 & -1/3 & 0 end{pmatrix}.
    $$







    share|cite|improve this answer












    share|cite|improve this answer



    share|cite|improve this answer










    answered Jan 14 at 9:06









    SouSou

    3,2892923




    3,2892923












    • $begingroup$
      Wow, nice! Tensors :P !!!
      $endgroup$
      – user2662833
      Jan 14 at 11:42










    • $begingroup$
      I just double checked your counter example, I don't believe $e^{ij} A_{ij} = e^{ij} B_{ij}$ In this example. have I made a mistake?
      $endgroup$
      – user2662833
      Jan 14 at 11:48










    • $begingroup$
      @user2662833 Just compute lhs and rhs separately by using the antisymmetry property (or not, whatever). E.g. lhs is $epsilon^{12}A_{12}+epsilon^{13}A_{13}+epsilon^{21}A_{21}+epsilon^{23}A_{23}+epsilon^{31}A_{31}+epsilon^{32}A_{32} = 2epsilon^{12}A_{12}+2epsilon^{13}A_{13}+2epsilon^{23}A_{23}=2$
      $endgroup$
      – Sou
      Jan 14 at 13:22


















    • $begingroup$
      Wow, nice! Tensors :P !!!
      $endgroup$
      – user2662833
      Jan 14 at 11:42










    • $begingroup$
      I just double checked your counter example, I don't believe $e^{ij} A_{ij} = e^{ij} B_{ij}$ In this example. have I made a mistake?
      $endgroup$
      – user2662833
      Jan 14 at 11:48










    • $begingroup$
      @user2662833 Just compute lhs and rhs separately by using the antisymmetry property (or not, whatever). E.g. lhs is $epsilon^{12}A_{12}+epsilon^{13}A_{13}+epsilon^{21}A_{21}+epsilon^{23}A_{23}+epsilon^{31}A_{31}+epsilon^{32}A_{32} = 2epsilon^{12}A_{12}+2epsilon^{13}A_{13}+2epsilon^{23}A_{23}=2$
      $endgroup$
      – Sou
      Jan 14 at 13:22
















    $begingroup$
    Wow, nice! Tensors :P !!!
    $endgroup$
    – user2662833
    Jan 14 at 11:42




    $begingroup$
    Wow, nice! Tensors :P !!!
    $endgroup$
    – user2662833
    Jan 14 at 11:42












    $begingroup$
    I just double checked your counter example, I don't believe $e^{ij} A_{ij} = e^{ij} B_{ij}$ In this example. have I made a mistake?
    $endgroup$
    – user2662833
    Jan 14 at 11:48




    $begingroup$
    I just double checked your counter example, I don't believe $e^{ij} A_{ij} = e^{ij} B_{ij}$ In this example. have I made a mistake?
    $endgroup$
    – user2662833
    Jan 14 at 11:48












    $begingroup$
    @user2662833 Just compute lhs and rhs separately by using the antisymmetry property (or not, whatever). E.g. lhs is $epsilon^{12}A_{12}+epsilon^{13}A_{13}+epsilon^{21}A_{21}+epsilon^{23}A_{23}+epsilon^{31}A_{31}+epsilon^{32}A_{32} = 2epsilon^{12}A_{12}+2epsilon^{13}A_{13}+2epsilon^{23}A_{23}=2$
    $endgroup$
    – Sou
    Jan 14 at 13:22




    $begingroup$
    @user2662833 Just compute lhs and rhs separately by using the antisymmetry property (or not, whatever). E.g. lhs is $epsilon^{12}A_{12}+epsilon^{13}A_{13}+epsilon^{21}A_{21}+epsilon^{23}A_{23}+epsilon^{31}A_{31}+epsilon^{32}A_{32} = 2epsilon^{12}A_{12}+2epsilon^{13}A_{13}+2epsilon^{23}A_{23}=2$
    $endgroup$
    – Sou
    Jan 14 at 13:22











    0












    $begingroup$

    Reason I asked is because of this example found from the book "A first course in string theory".



    enter image description here



    I don't understand the step when he cancels $epsilon$ on both sides because the dimension is generally bigger then 2 I think.






    share|cite|improve this answer











    $endgroup$













    • $begingroup$
      Here we must be careful that 8.55 follows from 8.22 which is a definition not an equality. So here we actually want to know what is the current looks like if we have such a Langrangian.
      $endgroup$
      – Sou
      Jan 14 at 14:01










    • $begingroup$
      I suppose the reason we can cancel $epsilon$ on both sides is because it consists of different parameters which are independent of each other. So we can vary one parameter on both sides keeping the other parameters constant. And therefore we can match terms even if we have a sum of terms on both sides. It's like the separation of variable method when solving partial differential equations.
      $endgroup$
      – Higgsino
      Jan 14 at 14:19
















    0












    $begingroup$

    Reason I asked is because of this example found from the book "A first course in string theory".



    enter image description here



    I don't understand the step when he cancels $epsilon$ on both sides because the dimension is generally bigger then 2 I think.






    share|cite|improve this answer











    $endgroup$













    • $begingroup$
      Here we must be careful that 8.55 follows from 8.22 which is a definition not an equality. So here we actually want to know what is the current looks like if we have such a Langrangian.
      $endgroup$
      – Sou
      Jan 14 at 14:01










    • $begingroup$
      I suppose the reason we can cancel $epsilon$ on both sides is because it consists of different parameters which are independent of each other. So we can vary one parameter on both sides keeping the other parameters constant. And therefore we can match terms even if we have a sum of terms on both sides. It's like the separation of variable method when solving partial differential equations.
      $endgroup$
      – Higgsino
      Jan 14 at 14:19














    0












    0








    0





    $begingroup$

    Reason I asked is because of this example found from the book "A first course in string theory".



    enter image description here



    I don't understand the step when he cancels $epsilon$ on both sides because the dimension is generally bigger then 2 I think.






    share|cite|improve this answer











    $endgroup$



    Reason I asked is because of this example found from the book "A first course in string theory".



    enter image description here



    I don't understand the step when he cancels $epsilon$ on both sides because the dimension is generally bigger then 2 I think.







    share|cite|improve this answer














    share|cite|improve this answer



    share|cite|improve this answer








    edited Jan 14 at 13:36

























    answered Jan 14 at 11:56









    HiggsinoHiggsino

    595




    595












    • $begingroup$
      Here we must be careful that 8.55 follows from 8.22 which is a definition not an equality. So here we actually want to know what is the current looks like if we have such a Langrangian.
      $endgroup$
      – Sou
      Jan 14 at 14:01










    • $begingroup$
      I suppose the reason we can cancel $epsilon$ on both sides is because it consists of different parameters which are independent of each other. So we can vary one parameter on both sides keeping the other parameters constant. And therefore we can match terms even if we have a sum of terms on both sides. It's like the separation of variable method when solving partial differential equations.
      $endgroup$
      – Higgsino
      Jan 14 at 14:19


















    • $begingroup$
      Here we must be careful that 8.55 follows from 8.22 which is a definition not an equality. So here we actually want to know what is the current looks like if we have such a Langrangian.
      $endgroup$
      – Sou
      Jan 14 at 14:01










    • $begingroup$
      I suppose the reason we can cancel $epsilon$ on both sides is because it consists of different parameters which are independent of each other. So we can vary one parameter on both sides keeping the other parameters constant. And therefore we can match terms even if we have a sum of terms on both sides. It's like the separation of variable method when solving partial differential equations.
      $endgroup$
      – Higgsino
      Jan 14 at 14:19
















    $begingroup$
    Here we must be careful that 8.55 follows from 8.22 which is a definition not an equality. So here we actually want to know what is the current looks like if we have such a Langrangian.
    $endgroup$
    – Sou
    Jan 14 at 14:01




    $begingroup$
    Here we must be careful that 8.55 follows from 8.22 which is a definition not an equality. So here we actually want to know what is the current looks like if we have such a Langrangian.
    $endgroup$
    – Sou
    Jan 14 at 14:01












    $begingroup$
    I suppose the reason we can cancel $epsilon$ on both sides is because it consists of different parameters which are independent of each other. So we can vary one parameter on both sides keeping the other parameters constant. And therefore we can match terms even if we have a sum of terms on both sides. It's like the separation of variable method when solving partial differential equations.
    $endgroup$
    – Higgsino
    Jan 14 at 14:19




    $begingroup$
    I suppose the reason we can cancel $epsilon$ on both sides is because it consists of different parameters which are independent of each other. So we can vary one parameter on both sides keeping the other parameters constant. And therefore we can match terms even if we have a sum of terms on both sides. It's like the separation of variable method when solving partial differential equations.
    $endgroup$
    – Higgsino
    Jan 14 at 14:19











    0












    $begingroup$

    8.22) which you asked for is the following relation.



    enter image description here






    share|cite|improve this answer









    $endgroup$


















      0












      $begingroup$

      8.22) which you asked for is the following relation.



      enter image description here






      share|cite|improve this answer









      $endgroup$
















        0












        0








        0





        $begingroup$

        8.22) which you asked for is the following relation.



        enter image description here






        share|cite|improve this answer









        $endgroup$



        8.22) which you asked for is the following relation.



        enter image description here







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Jan 14 at 14:23









        HiggsinoHiggsino

        595




        595















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