Cascaded IIR filter design

[Markus Svilans]

Hello,

I would like to use Scilab to design a cascaded IIR filter.

I'm able to design a filter using iir(), as in the following example
code:

ystr=[ 'type (lp, hp, bp, sb) ';
    'order (integer)';
    'design (butt, cheb1, cheb2 , ellip)' ;
    'cut-off frequencies (2-vector in [0, 0.5])';
    'error values  0 delta(1),delta(2) 1 '];
w = x_mdialog('Choose filter type and parameters',...
    ystr,['bp';'3';'ellip';'0.15 0.25';'0.08 0.035'])

if w<>[] then
  hz=iir(evstr(w(2)),w(1),w(3),evstr(w(4)),evstr(w(5)));
  [hzm,fr]=frmag(hz,256);
  xselect();
  plot2d(fr',hzm')
  xtitle('Discrete IIR filter '+'( '+ w(3)+' ) ',' ',' ');

  hz
end

My question is, how can I convert the z domain expression in hz to a
set of coefficients suitable for use in a cascaded IIR filter
implementation? Any help would be greatly appreciated.

Best regards,
Markus.

(also posted in the comp.soft-sys.math.scilab group)