Is Aijkl a Symmetric Rank 4 Tensor? Proof Needed!

In summary, the problem involves a rank 4 square tensor Aijkl with three given symmetries and the task is to prove that it also satisfies the symmetry A_{ijkl} = A_{klij}. Using the given symmetries, it can be shown that A_{ijkl} + A_{iljk} = A_{klij} + A_{kjli}. Further rearranging and using the first and second symmetries, A_{jilk} + A_{jkil} = A_{lkji} + A_{likj} can be obtained. Using the third symmetry, this simplifies to A_{jilk} = A_{lkji}. This is equivalent to the required symmetry A_{ijkl} =
  • #1
Ressurection
7
0

Homework Statement


Let Aijkl be a rank 4 square tensor with the following symmetries:
[tex]
A_{ijkl} = -A_{jikl}, \qquad A_{ijkl} = - A_{ijlk}, \qquad A_{ijkl} + A_{iklj} + A_{iljk} = 0,
[/tex]

Prove that
[tex]
A_{ijkl} = A_{klij}
[/tex]

Homework Equations

The Attempt at a Solution


From the first two properties I concluded that:
[tex]
A_{iikl} = 0 \qquad A_{ijkk} = 0
[/tex]

The last one leaded me to:
[tex]
A_{ikli} = -A_{ilik} \qquad A_{ikkj} = -A_{ikjk}
[/tex]

However I don't see how this last one may help me.
 
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  • #2
I suggest not trying to make any contractions and instead just apply the given symmetries, including the last one involving three tensor components.
 
  • #3
New attempt, got further but still missing something, hope this was what you meant.
From the third property:
[tex] A_{ijkl} + A_{iklj} + A_{iljk} = 0 [/tex]
[tex] A_{klij} + A_{kijl} + A_{kjli} = 0 [/tex]
Therefore:
[tex] A_{ijkl} + A_{iklj} + A_{iljk} = A_{klij} + A_{kijl} + A_{kjli} [/tex]
Since the first two properties refer to switching the first pair or the last pair of indexes, I can write:
[tex] A_{ijkl} + A_{kijl} + A_{iljk} = A_{klij} + A_{kijl} + A_{kjli} [/tex]
Leading to
[tex] A_{ijkl} + A_{iljk} = A_{klij} + A_{kjli} [/tex]
However I still have one extra term on each side that I can't deal with the same way as before.
 
  • #4
Ressurection said:
[tex] A_{ijkl} + A_{iljk} = A_{klij} + A_{kjli} [/tex]
However I still have one extra term on each side that I can't deal with the same way as before.

What do you get if you simply do the following renaming of the indices in this equation: ##i \leftrightarrow j##, ##k \leftrightarrow \ell##? Does it remind you of something?
 
  • #5
That would result in:
[tex] A_{jilk} + A_{jkil} = A_{lkji} + A_{likj} [/tex]
The only thing it reminds me is of the third symmetry again, but if I use it I end up with a meaningless result:
[tex] A_{jlki} = A_{ljik} [/tex]
Which translates in the first two symmetries.
 
  • #6
Ressurection said:
The only thing it reminds me is of the third symmetry again

Try using the first and second symmetries instead. Also, it will help if you put all of the components on one side and equate to zero.
 
  • #7
Finally got it! Thanks a lot for the help
 

FAQ: Is Aijkl a Symmetric Rank 4 Tensor? Proof Needed!

What is a Rank 4 Tensor Symmetry Proof?

A Rank 4 Tensor Symmetry Proof is a mathematical demonstration that shows the symmetry properties of a rank 4 tensor. A rank 4 tensor is a mathematical object that represents a multidimensional array of numbers, and its symmetry refers to the invariance of its values under certain transformations.

Why is a Rank 4 Tensor Symmetry Proof important?

A Rank 4 Tensor Symmetry Proof is important because it allows us to better understand the properties of rank 4 tensors and how they behave under different transformations. This is crucial in many scientific fields, such as physics and engineering, where tensors are used to describe physical quantities and their relationships.

What are the common methods used to prove symmetry of a Rank 4 Tensor?

The most common methods used to prove symmetry of a Rank 4 Tensor include the direct method, where the symmetry conditions are evaluated directly, and the use of index notation, where the symmetry conditions are expressed in terms of indices and their corresponding values. Other methods include the use of symmetry operations and transformation matrices.

How is a Rank 4 Tensor Symmetry Proof used in real-world applications?

A Rank 4 Tensor Symmetry Proof is used in various real-world applications, such as in fluid mechanics, electromagnetism, and finite element analysis. In these fields, tensors are used to model and analyze complex systems and their symmetries play a crucial role in accurately describing the behavior of these systems.

Are there any limitations to the Rank 4 Tensor Symmetry Proof?

While the Rank 4 Tensor Symmetry Proof is a powerful tool, it does have some limitations. It may not be applicable to tensors with non-numeric elements, such as symbolic or variable elements. Additionally, the proof may become increasingly complex for higher-order tensors, making it difficult to apply in certain cases.

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