How to input the modulus of gradients

General Discussion
1

Hi,
I want to write it:

屏幕截图 2024-03-17 172556

I code as:

macro msquare(u) (dx(u)^2+dy(u)^2)//
mesh Th = buildmesh(c1(10)+c2(10)+c3(10)+c4(10));
fespace Vh(Th,P1);
Vh u,w,oldu,q,f;
Vh v,oldv;
problem fcv([u,v],[w,q])=
        -int2d(Th)(v*w)
        -int2d(Th)(1-0.5*(msquare(u)+msquare(oldu));

But it’s wrong:
Error line number 9, before token +

current line = 9
Compile error :
line number :9, +
error Compile error :
line number :9, +
code = 1 mpirank: 0

line 9 is macro msquare(u) (dx(u)^2+dy(u)^2)//

How can I solve it.
Thank you in advance.

2

Not a linear system.

Didn’t multiply by test functions.