EC=1^2;
ES=3.8^2;
ER=5.20^2;
landa=1.55;
k0=2*pi/landa;
hx=0.05;
hy=0.05;
hx=0.05;
xlo=20;
xhi=35;
ylo=15;
yhi=45;
NX=50;
NY=59;
prm=EC*ones(NX,NY);
prm([1:xlo-1],:)=ES*ones(xlo-1,NY);
prm([xlo+1:xhi-1],[ylo+1:yhi-1])=ER*ones(xhi-xlo-1,yhi-ylo-1);
prm(xlo)=0.5*(prm(xlo-1)+prm(xlo+1))...