Is Aijkl a Symmetric Rank 4 Tensor? Proof Needed!

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Homework Help Overview

The discussion revolves around the properties of a rank 4 square tensor, Aijkl, and its symmetries. Participants are tasked with proving a specific equality involving the tensor based on given symmetry conditions.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the implications of the tensor's symmetry properties, attempting to derive relationships between its components. Some express uncertainty about how to utilize the symmetries effectively, while others suggest focusing on specific properties without making contractions.

Discussion Status

The conversation has progressed with participants sharing their attempts and insights. Some have proposed renaming indices to explore relationships further, while others have suggested alternative approaches to consolidate terms. There is a collaborative effort to clarify reasoning and explore different angles, though no consensus has been reached yet.

Contextual Notes

Participants are working within the constraints of the problem statement and the specific symmetries provided, questioning how these affect their reasoning and conclusions.

Ressurection
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Homework Statement


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

Prove that
<br /> A_{ijkl} = A_{klij}<br />

Homework Equations

The Attempt at a Solution


From the first two properties I concluded that:
<br /> A_{iikl} = 0 \qquad A_{ijkk} = 0<br />

The last one leaded me to:
<br /> A_{ikli} = -A_{ilik} \qquad A_{ikkj} = -A_{ikjk}<br />

However I don't see how this last one may help me.
 
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I suggest not trying to make any contractions and instead just apply the given symmetries, including the last one involving three tensor components.
 
New attempt, got further but still missing something, hope this was what you meant.
From the third property:
A_{ijkl} + A_{iklj} + A_{iljk} = 0
A_{klij} + A_{kijl} + A_{kjli} = 0
Therefore:
A_{ijkl} + A_{iklj} + A_{iljk} = A_{klij} + A_{kijl} + A_{kjli}
Since the first two properties refer to switching the first pair or the last pair of indexes, I can write:
A_{ijkl} + A_{kijl} + A_{iljk} = A_{klij} + A_{kijl} + A_{kjli}
Leading to
A_{ijkl} + A_{iljk} = A_{klij} + A_{kjli}
However I still have one extra term on each side that I can't deal with the same way as before.
 
Ressurection said:
A_{ijkl} + A_{iljk} = A_{klij} + A_{kjli}
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?
 
That would result in:
A_{jilk} + A_{jkil} = A_{lkji} + A_{likj}
The only thing it reminds me is of the third symmetry again, but if I use it I end up with a meaningless result:
A_{jlki} = A_{ljik}
Which translates in the first two symmetries.
 
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.
 
Finally got it! Thanks a lot for the help
 

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