function Er2 = graphe2D(n0,nbIt)

Er2=zeros(nbIt,1)';
n=n0;
for iter=1:nbIt
    n=n+5 ;
    % Creation du laplacien:
    A2=Laplacien2D(n);

    %Creation d'une solution exacte
    x=[1/n/n:1/n/n:1]'; y=x;
    SolEx=sin(pi*x).*sin(pi/2*y);
    % Calcul du 2nd mbre
    F=A2*SolEx;

    % Resolution
    U=SolChol(A2,F);

    % Graphe
    UU=zeros(n,n);
    for i=1:n
      for j=1:n
         UU(i,j)=U((i-1)*n+j);
      end
    end
    [x, y]=meshgrid(1/n:1/n:1);

    % Etude de l'erreur:
    Erreur=U-SolEx;
    E2=norm(Erreur,2);
    Er2(iter)=E2;
    
end

subplot(2,2,1);
surf(x,y,UU,UU);
subplot(2,2,2);
hold on 
  plot(1:1:size(U),U,'or');
  plot(SolEx,'.b');
hold off
subplot(2,2,3);
plot(n0:5:n0+5*nbIt-5,Er2,'+g');
