function phix=phitv(zet)
%modified 3/19/98 to allow vector input/output by Peter Guest 

%stable cases
	x=1+4.7*zet;
   phix=x;
	

%unstable cases
        uns=find(zet<0 &zet>-1);    % &zet>-.2
        if ~isempty(uns);
            y=1./(1-16.*zet(uns)).^.5;
            phix(uns)=y;
           
        end; 
		  unx=find(zet<=-1);
			 if ~isempty(unx);
           yy=1./(-28.86-98.96.*zet(unx)).^.33;
            phix(unx)=yy;
           
        end; 
     
