Symbolic computation of gradient

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SUMMARY

This discussion focuses on symbolic computation techniques for efficiently calculating gradients with respect to vectors. The user seeks shortcuts that avoid element-wise differentiation, specifically referencing the gradient of the function \(\nabla_x \left( \frac{1}{|{\bf x}^{'} - {\bf x}|} \right)\) and its simplification. The conversation highlights the effectiveness of using symbolic manipulation, such as recognizing \(\sqrt{x^Tx}=|x|\), to derive gradients more swiftly. The method discussed demonstrates that leveraging symbolic ideas can significantly streamline the computation process.

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I'm wondering if there are any convenient symbolic "shortcuts" (i.e. abuse of notation) that enable one to compute the gradient with respect to a certain vector, without decomposing the computation into the vector's individual elements and differentiating with respect to each element. For example:
[tex] \nabla_x \left( \frac{1}{|{\bf x}^{'} - {\bf x}|} \right) = \frac{{\bf x}^{'} - {\bf x}}{|{\bf x}^{'} - {\bf x}|^3}[/tex]
Besides the obvious method of evaluating [tex]\frac{\partial}{\partial x_1}[/tex] and so on, is there a faster method of symbolic computation?
 
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If you consider
[tex]\sqrt{x^Tx}=|x|[/tex]
then symbolic ideas help to get to the final expression:

[tex]\nabla_x \left( (x'-x)^{T}(x'-x) \right)^{-1/2} = \left( (x'-x)^{T}(x'-x) \right)^{-3/2} (x'-x)[/tex]
 
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Yes, that works very well. Thanks a lot.
 

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