Can transformation coefficients be interchanged in symmetric tensors?

In summary, the lecture notes state that if a tensor is symmetric in one coordinate system, it remains symmetric in all coordinate systems. This is shown through a proof where the exchange of indices is allowed due to the symmetry of the tensor. The question regarding the validity of changing the order of transformation coefficients is answered by the fact that the tensor is symmetric.
  • #1
spacetimedude
88
1

Homework Statement


The lecture notes states that if ##T_{ij}=T_{ji}## (symmetric tensor) in frame S, then ##T'_{ij}=T'_{ji}## in frame S'. The proof is shown as $$T'_{ij}=l_{ip}l_{jq}T_{pq}=l_{iq}l_{jp}T_{qp}=l_{jp}l_{iq}T_{pq}=T'_{ji}$$ where relabeling of p<->q was used in the second equality. Where I am confused is that after the 3rd equality, the order of ##l_{iq}## and ##l_{jp}## changes. Is this allowed in all tensors?
Thanks in advance
 
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  • #2
The ##l_{jp}## are just numbers so your question boils down to "is ##xy = yx##?" where ##x## and ##y## are real numbers.
 
  • #3
Since the tensor is symmetric then you can interchange the i and j in the expression.

Right?
 
  • #4
jedishrfu said:
Since the tensor is symmetric then you can interchange the i and j in the expression.

Right?
The idea was to show that a tensor with symmetric components in one coordinate system has symmetric components in all coordinate systems. Above this meand that the exchange of p and q in ##T_{pq}## is assumed to be fine and we want to show that this implies that i and j can be exchanged. The OP's question was regarding the validity of changing the order of the transformation coefficients.
 
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Related to Can transformation coefficients be interchanged in symmetric tensors?

1. What is a symmetric tensor?

A symmetric tensor is a mathematical object that represents a physical quantity or property that remains unchanged when the coordinate system is rotated or reflected. It is a type of tensor that is characterized by having equal values for certain components that are related by symmetry.

2. How is invariance related to symmetric tensors?

Invariance refers to the property of remaining unchanged under certain transformations. In the case of symmetric tensors, invariance means that the tensor remains the same when the coordinate system is rotated or reflected, regardless of the specific values of the components.

3. What are the applications of symmetric tensors?

Symmetric tensors have a wide range of applications in physics, engineering, and other fields. They are commonly used in mechanics, electromagnetism, and fluid dynamics to represent physical quantities such as stress, strain, and electric fields. They are also used in image and signal processing, as well as in materials science and computer graphics.

4. How do you determine if a tensor is symmetric?

To determine if a tensor is symmetric, you can use the symmetry conditions for each component. For a second-order symmetric tensor, the condition is that the components must be equal when the indices are swapped. For higher-order tensors, there are more conditions to check, but the principle remains the same.

5. Can symmetric tensors be used to simplify calculations?

Yes, symmetric tensors can often be used to simplify calculations, since they have fewer independent components than general tensors. This allows for a more efficient representation of physical quantities and can lead to simpler and more elegant solutions to problems.

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