	function y=rexa(E)
	v0=1;a=100;L=5;
	k1=sqrt(2*E); k2=sqrt(2*(E-v0)); 
	rex = (k1.^2-k2.^2).*sin(k2*L)./...
	((k1.^2+k2.^2).*sin(k2*L)+2i*k1.*k2.*cos(k2*L));
	y = abs(rex).^2;
	end