Partial Fraction Expansion: residued.m

Figure J.6 gives a listing of a matlab function for computing a ``right justified'' partial fraction expansion (PFE) of an IIR digital filter $H(z)=B(z)/A(z)$ as described in §6.8 (and below).

The code in Fig.J.6 was written for Octave, and should also work in Matlab if the 'e' output argument containing pole multiplicities is omitted (in two places).

Figure J.6: Matlab/Octave function for computing a partial fraction expansion in which the parallel sections follow the FIR part.

 

function [r, p, f, e] = residued(b, a, toler)
if nargin<3, toler=0.001; end
NUM = b(:)';
DEN = a(:)';
nb = length(NUM);
na = length(DEN);
f = [];
if na<=nb
  f = filter(NUM,DEN,[1,zeros(nb-na)]);
  NUM = NUM - conv(DEN,f);
  NUM = NUM(nb-na+2:end);
end
[r,p,f2,e] = residuez(NUM,DEN,toler);