# Incompatible boundary conditions in parallel FreeFEM

Hi,
I am trying to test FreeFem parallel (combined with PETSc) by solving the following linear elastic problem:

• a 2D truss is clamped at the left end and loaded at the right end with a surface force pointing downwards.
• the geometry is constructed as follows:
``````// Domain of admissible shapes: mesh parameters
real L=2.;                                                         // length [m]
real H=1.;                                                         // height [m]
int nel=80;                                                      // mesh density

/* Domain Mesh */
mesh Dh;
int Tn0=0;                       // label denoting the free part of the boundary
int Tn1=1;                     // label denoting the loaded part of the boundary
int Td0=10;                     // label denoting the fixed part of the boundary

if (!mpirank) {
if (verbosity) cout<<"  Domain Mesh Generation"<<endl;
Dh=square(int(L)*nel, int(H)*nel, [L*x,H*y], flags=1);

{ func nlabel=(y<1.e+2)? Tn0: label; Dh=change(Dh, flabel=nlabel);}
{ func nlabel=(x<1.e-5)? Td0: label; Dh=change(Dh, flabel=nlabel);}
{ func nlabel=(x>(L-1.e-5) && y>(H/2-H*0.05) && y<(H/2+H*0.05))? Tn1: label;
Dh=change(Dh, flabel=nlabel);}
}

meshN DhG=Dh;                                                     // global mesh

int[int] n2o;
macro DhN2O() n2o // EOM    // keep local to global correspondance in buildDmesh
buildDmesh(Dh);                                          // domain decomposition
``````

As I solve the problem using 4 nodes, I get the following message:

``````  Elasticity problem
Warning: -- Your set of boundary condition is incompatible with the mesh label.
Warning: -- Your set of boundary condition is incompatible with the mesh label.
Warning: -- Your set of boundary condition is incompatible with the mesh label.
--- system solved with PETSc (in 2.025411e+00)
``````

When I look at Dh in Paraview for example, I see that Tn1 is only existing in one of the 4 subdomains… hence 3 warning messages.

The problem may come from the ways labels are propagated in buildDmesh… I would be grateful if you could you help me correct the domain decomposition part such that this error disappears. If needed, I can provide the full code (176 lines).

This is not an error, just a warning, that can be turned off with `verbosity = 0;` before the assembly.