Matrix in two dimension of space

can anyone help in this question please

i found in a code FF++ in one dimension of space the follwing instructions:

int Nbx=1e4;
real tau=10.;
meshL Th=segment(Nbx,[x*L,0.]);
fespace Vh(Th,typeFE);
Vh I0;
Vh Itmtau=oldI,Itausave;
int ntau=(tau)/dt;
real[int,int] Itau(Vh.ndof,ntau+2);
int op=0,ittau=0,ittmtau=0;
int it,itsave;

My question is: what are the changes
to be made on this piece of code when we are in 2D of space:
real H=20., L=20.;
mesh Th = square(N,N,[Lx,Hy]);

This is a good way to start.

So what are the changes we have to do in 2D? Please