% Program 9_4
%  Computation of the output noise variance due
%  to input quantization of a digital filter
%  based on a partial-fraction approach
%
num = input('Type in the numerator = ');
den = input('Type in the denominator = ');
[r,p,K] = residue(num,den); % partial fraction expansion
R = size(r,1);
R2 = size(K,1);
if R2 > 1
   disp('Cannot continue...');
   return;
end

if R2 == 1
   nvar = K^2;
else
   nvar = 0;
end
% Compute output noise variance
for k = 1:R,
   for m = 1:R,
      integral = r(k)*conj(r(m))/(1-p(k)*conj(p(m)));
      nvar = nvar + integral;
   end
end
disp('Output Noise Variance = ');disp(real(nvar));