Number of degrees of freedom

Dear all

I like to limit my integration over a portion of whole.
To do this I changed int2d(Th) to int2d(Th,Coil)

varf vPoi(u,v)
    =int2d(Th,Coil) (sig * Grad(u)' * Grad(v))
    +on(CoilTerminalIn, u=0)
    +on(CoilTerminalOut, u=1);
matrix Poi = vPoi(Ph,Ph);
cout << "sizePoi " << Poi.n << endl;

The problem is that the size of matrix Poi does not vary at all.
How can i remove extra variables?

mesh ThCoil = trunc(Th, region == Coil);
varf vPoi(u,v)
    =int2d(ThCoil) (sig * Grad(u)' * Grad(v))//'
    +on(CoilTerminalIn, u=0)
    +on(CoilTerminalOut, u=1);
fespace PhCoil(ThCoil, P1);
matrix Poi = vPoi(PhCoil,PhCoil);
cout << "sizePoi " << Poi.n << endl;
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It seems I had a misunderstanding about int2d

suppose that I have a mixed fespace like
fespace -> [RT0Orth,P1]
I like to have RT0Orth to be defined all over the domain and P1 only inside the coil.

In fact I like to make a matrix like K=[A B; B' C] which

just defined VRT and VP1 fespae
difined you matrix A, B and C with varf, va, vb,vc;
varf va([u1,u2],[v1,v2]) = … ;
varf vb(p,[v1,v2]) = …;
varf vc(p,q) = …;

matrix A = va(VRT,VRT);
matrix B = vb(VP1,VRT);// warning test function corresponding to row index.
matrix C = vb(VP1,VP1);

matrix K = [[A,B],[B’,C]];

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