Help with Levi-Civita manipulation

In summary, the given expression can be written in vectorial form by applying the product rule and using the Kronecker delta to express the partial of x_m. This allows for the resolution of the result into vector form. The Einstein summation convention was used in the derivation of the expression.
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user1139
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Confused as to how I can obtain a divergence term by manipulating using Levi-Civita
How do I write the following expression

$$\epsilon_{mnk} J_{1n} \partial_i\left[\frac{x_m J_{2i}}{|\vec{x}-\vec{x}'|}\right]$$

back into vectorial form?

Einstein summation convention was used here.

Context: The above expression was derived from the derivation of torque on a general current distribution. It is part of an expression obtained by considering
$$\left[\left(\vec{x}\times\vec{J}_1(\vec{x}')\right)\left(\vec{J}_2(\vec{x})\cdot\vec\nabla\frac{1}{|\vec x-\vec x'|}\right)\right]_k$$

My source of confusion is that I am suppose to obtain a divergence term from the first expression but there is the $x_m$ term in the square brackets. As such, I am unsure of how to proceed.
 
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  • #2
Apply the product rule, and use Kronecker delta to express partial of ##x_m##:
[tex] \partial_i \left[ x_m J_{2i} \frac{1}{|\vec{x}-\vec{x}'|}\right] = \delta_{m i} J_{2i}\frac{1}{|\vec{x}-\vec{x}'|} + x_m J_{2i}\partial_i \left[ \frac{1}{|\vec{x}-\vec{x}'|}\right][/tex]
where ##\partial_i x_j = \delta_{ij}## and ##\delta_{ij} = 1## if ##i=j## otherwise ##=0##.

You should then be able to resolve the result in vector form.
 
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1. What is Levi-Civita manipulation?

Levi-Civita manipulation is a mathematical technique used to simplify and manipulate complicated equations involving tensors. It involves using the properties of the Levi-Civita symbol, which represents the sign of a permutation, to simplify tensor equations.

2. How is Levi-Civita manipulation used in physics?

Levi-Civita manipulation is commonly used in physics, particularly in the study of vector and tensor fields. It is used to simplify equations involving these fields and to solve problems in electromagnetism, general relativity, and fluid mechanics.

3. What are some common properties of the Levi-Civita symbol?

The Levi-Civita symbol has three main properties: it is completely antisymmetric, it is nonzero only when all of its indices are unique, and it has a value of 1 or -1 depending on the number of permutations needed to order its indices.

4. Can Levi-Civita manipulation be applied to any tensor equation?

Yes, Levi-Civita manipulation can be applied to any tensor equation. However, it is most commonly used for equations involving second-order tensors, such as the stress tensor or the electromagnetic field tensor.

5. Are there any limitations to using Levi-Civita manipulation?

One limitation of Levi-Civita manipulation is that it can only be applied to equations involving tensors with an odd number of indices. It is also important to note that Levi-Civita manipulation is just one tool in a mathematician's or physicist's toolkit and may not always be the most efficient or appropriate method for solving a problem.

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