How Does Symmetry Impact the Derivative in Tensor Calculations?

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SUMMARY

The discussion focuses on the impact of symmetry in tensor calculations, specifically in deriving the expression for the partial derivative of the scalar function \(\phi = a_{rs}x^{r}x^{s}\). The correct derivative is established as \(\frac{\partial\phi}{\partial x^{r}} = (a_{rs} + a_{sr})x^{s}\). Key to this derivation is the understanding that once an index is summed over, it cannot be reused in the differentiation process. Participants emphasized the importance of correctly applying index notation to avoid errors.

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  • Knowledge of symmetry properties in tensors
  • Experience with index summation conventions
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Homework Statement


If \phi=a_{rs}x^{r}x^{s}
Then show that \frac{\partial\phi}{\partial x^{r}}=(a_{rs}+a_{sr})x^{s}

Homework Equations





The Attempt at a Solution


Help please I can't seem to get the correct answer. Thanks
 
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hi adriang! :smile:

you have to remember that once you've summed over an index, you can't use it again! :rolleyes:

in this case, you can't write ∂/∂xr (arsxrxs) …

instead try writing ∂/∂xr (aqsxqxs) :wink:
 
ah thanks tim lol silly me..
 

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