% SCHRI4 Symbolic modification by a linear divisor
%
function ab=schri4(N,ab0,z,rho0)
N0=size(ab0,1);
if N0<N, error('input array too short'), end
r(1)=rho0;
for k=1:N
  r(k+1)=z-ab0(k,1)-ab0(k,2)/r(k);
end
ab(1,1)=ab0(1,1)+r(2); ab(1,2)=-r(1);
if N==1, return, end
for k=2:N
  ab(k,1)=ab0(k,1)+r(k+1)-r(k);
  ab(k,2)=ab0(k-1,2)*r(k)/r(k-1);
 end
