## I need to find the gradient of this norm

Hi. I have some problem in finding the gradient of this norm

$\sum_{l = 1}^{n} \left ( (\nabla_{x} u)^{2}_{l} + (\nabla_{y} u)^{2}_{l} \right )^{1/2}$

I have some results to it but I'm not sure about it.
Can you give me some insights for this. Thanks.
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