How i can programming this term

Hello everyone, i need help because, i am begineer in Freefem++
There are someone can help me, how i can programming this term


where |u| is the norm on the unknown function
|u| = sqrt(ux^² + uy)
Thank you

The L_2 norm of a vector u is defined as |u| = (\int_{\Omega} u*u d{\Omega))^{1/2}.
You can calculate it as follows (I assume that you are working in finite element space and
have a mesh on your domain in 2D).
|u| = sqrt(int2d(Th)(u*u))


Thank you so much,
yes, i work in Finite Element space and the domain 2D.