int n=20,nn=n+10;
real[int] xx(nn),yy(nn);
// build square $]-1,1[^2$
mesh Th2=square(2,2,[2*x-1,2*y-1]); 
mesh Th=square(100,100,[2*x-1,2*y-1]); 
fespace Wh(Th2,P0edge);
Wh w=0;

fespace Vh(Th,P1);

w[]=0;
w[][6]=1;
Vh u=w;

plot(u,Th2,wait=1);
   savemesh(Th,"mm",[x,y,u*.5]); //  save mm.points and mm.faces file for medit
   // build a mm.bb file 
	{ ofstream file("mm.bb"); 
	file << "2 1 1 "<< u[].n << " 2 \n";
	int j;
	for (j=0;j<u[].n ; j++)  
	  file << u[][j] << endl; 
    }  
    // call ffmedit command 	
    exec("ffmedit mm");
    // clean files
    exec("rm mm.bb mm.faces mm.points");