function [Kz,ind]=eikon(signgf,gf2,gkx2,s2,sc)
% code by: Ruiqing He, University of Utah, 2004

if nargin == 4; sc=1; end

ws2=gf2*s2;
ind=gkx2<(sc*sc*ws2);

Kz=ws2-gkx2; 
Kz=signgf.*sqrt(Kz.*ind);



