Why Doesn't the Tensor Identity Work Out?

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SUMMARY

The tensor identity a·Tb = b·TTa is a fundamental concept in continuum mechanics that holds true for all tensors. The discussion reveals confusion regarding the application of the dot product and the order of operations. It is confirmed that the identity is correct and serves as a basis for further mathematical proofs. Proper understanding of vector algebra, particularly the commutative property, is essential for correctly applying this identity.

PREREQUISITES
  • Understanding of tensor notation and operations
  • Familiarity with continuum mechanics principles
  • Knowledge of vector algebra, specifically the commutative property
  • Experience with mathematical proofs involving tensors
NEXT STEPS
  • Study the properties of tensors in continuum mechanics
  • Learn about the commutative property in vector algebra
  • Explore mathematical proofs that utilize the tensor identity
  • Practice problems involving tensor operations and identities
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Students and educators in continuum mechanics, mathematicians focusing on tensor calculus, and anyone seeking to deepen their understanding of tensor operations and identities.

QuickLoris
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My textbook (regarding continuum mechanics) has the following identity that is supposed to be true for all tensors:

a[itex]\cdot[/itex]Tb = b[itex]\cdot[/itex]TTa

But I don't get the same result for both sides when I work it out.
For each side, I'm doing the dot product last. For example, I compute Tb first and then computer the dot product of a[itex]\cdot[/itex]Tb. Is that right? I tried doing it the other way around also, but it didn't work out that way either.

I'm still pretty new to this subject and teaching it to myself, so I figure I'm multiplying something incorrectly, but I don't understand what.
 
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QuickLoris said:
My textbook (regarding continuum mechanics) has the following identity that is supposed to be true for all tensors:

a[itex]\cdot[/itex]Tb = b[itex]\cdot[/itex]TTa

But I don't get the same result for both sides when I work it out.


I don't know what you might be doing wrong, but vector algebra is commutative, as you say.

QuickLoris said:
For each side, I'm doing the dot product last. For example, I compute Tb first and then computer the dot product of a[itex]\cdot[/itex]Tb. Is that right?

The original identity is definitely correct, as it is a common one used as a starting point for other math proofs.
 

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