Dear FreeFem++ community,

For domain decomposition, I need to solve a 2d problem with a given function g on a boundary (thus 1d) obtained with an iterative finite element calculation. g can be, for example, the restriction of a finite element function on a boundary.

In the example below, g is defined in the whole finite element space, I would like to define it only on the top interface. Perhaps with 1d meshL ?

```
border top(t=0,1){x=t;y=1;}
border right(t=0,1){x=1;y=1-t;}
border bottom(t=0,1){x=1-t;y=0;}
border left(t=0,1){x=0;y=t;}
mesh Th=buildmesh(top(-5)+right(-5)+bottom(-5)+left(-5));
fespace Vh(Th,P1);
Vh g = x*y;
Vh u,v;
solve Prob(u,v)
= int2d(Th)(dx(u)*dx(v) + dy(u)*dy(v))
+ on(right, bottom, left, u=0)
+ on(top, u=g);
plot(u, wait=1, value=1);
```