# Issue with boundary conditions on a basic example

**URL:** <https://community.freefem.org/t/issue-with-boundary-conditions-on-a-basic-example/271>\
**Category:** General Discussion\
**Created:** [February 26, 2020, 10:47am UTC](https://community.freefem.org/t/issue-with-boundary-conditions-on-a-basic-example/271 "2020-02-26T10:47:23Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Mordokkai](https://avatars.discourse-cdn.com/v4/letter/m/f6c823/32.png) [@Mordokkai](https://community.freefem.org/u/Mordokkai)\
**Post date:** [February 26, 2020, 10:47am UTC](https://community.freefem.org/t/issue-with-boundary-conditions-on-a-basic-example/271/1 "2020-02-26T10:47:23Z")

</div>

Hi all,

I have a warning I don’t understand about my boundary conditions:  
Warning: – Your set of boundary condition is incompatible with the mesh label.

The basic example I’m testing is the following:

border a(t=0, dims[0]){x=t; y=0; label=1;};  
border b(t=0, dims[1]){x=dims[0]; y=t; label=2;};  
border f(t=0, dims[0]){x=dims[0]-t; y=dims[1]; label=3;};  
border d(t=0, dims[1]){x=0; y=dims[1]-t; label=4;};  
n = 3;  
mesh fm = buildmesh(a(n) + b(n) + f(n) + d(n));  
fespace Vh(fm, P1);  
func real heatsource(){  
return 1;  
}  
Vh u, v;  
Vh myHeat = heatsource();  
problem heat(u,v) = int2d(fm)(dx(u)\*dx(v) + dy(u)_dy(v)) - int2d(fm)(myHeat_v)  
+ on(a, u=0)  
+ on(b, u=0)  
+ on(f, u=0)  
+ on(d, u=0);  
heat;

Do you have any idea which mistake did I do ?

Sylvain

---

<div class="post-metadata">

**Author:** ![prj](https://avatars.discourse-cdn.com/v4/letter/p/ecae2f/32.png) [@prj](https://community.freefem.org/u/prj)\
**Post date:** [February 26, 2020, 10:50am UTC](https://community.freefem.org/t/issue-with-boundary-conditions-on-a-basic-example/271/2 "2020-02-26T10:50:10Z")

</div>

```auto
+ on(a, u=0)
+ on(b, u=0)
+ on(f, u=0)
+ on(d, u=0);

```

should read

```auto
+ on(1, u=0)
+ on(2, u=0)
+ on(3, u=0)
+ on(4, u=0);

```

---

<div class="post-metadata">

**Author:** ![Mordokkai](https://avatars.discourse-cdn.com/v4/letter/m/f6c823/32.png) [@Mordokkai](https://community.freefem.org/u/Mordokkai)\
**Post date:** [February 26, 2020, 10:51am UTC](https://community.freefem.org/t/issue-with-boundary-conditions-on-a-basic-example/271/3 "2020-02-26T10:51:51Z")

</div>

Indeed, no warning anymore, thanks a lot 🙂