
function psi=psi_fu(zet)
	
   psi=3.9*(1./(1-20*zet).^.333-zet-1./(7-zet)).^.667;    
   uns=find(zet>0);
if ~isempty(uns)
	psi(uns)=.92*3.9*(1+2.5*zet(uns).^.667);

end;