function [F,G,D,C]=sc2d(G,V,T)
G=ss(G); G=balreal(G); A=G.a; B=G.b; C=G.c;
[F,G]=c2d(A,B,T); V0=B*V*B'*T; Vd=V0;
vmax=sum(sum(abs(Vd))); vv=vmax; i=1;
while (1)
   V1 = T/(i+1)*(A*V0+V0*A'); v0 = sum(sum(abs(V1)));
   Vd = Vd+V1; V0 = V1; vv = [vv v0]; i=i+1;
   if v0 < 1e-10*vmax, break; end
end
[U,S,V0]=svd(Vd); V0=sqrt(diag(S));
Vd=diag(V0); D=U*Vd;