function [b,a] = imp_invr(c,d,T)
% Impulse Invariance Transformation from Analog to Digital Filter
% ------------------------------------------------------------------
% [b,a] = imp_invr(c,d,T)
% b = Numerator polynomial in z^(-1) of the digital filter
% a = DEnominator polynomial in z^(-1) of the analog filter
% c = Numerator polynomial in s of the analog filter
% d = DEnominataor polynomial in s if the analog filter
% T = Sampling (transformation) parameter
%
[R,p,k] = residue(c,d)
p = exp(p*T);
[b,a] = residuez(R,p,k);
b = real(b');
a = real(a');