%% this function set up a order 3 elliptic lowpass
%% use ellip from the SP toolbox
%% [B,A]=ellip(3,      3,              50,              0.35) 
%%            order; passband ripple; stopband ripple; cut off frequency 
%% results:
A = [ 1  -1.59212298544274   1.38724212079689  -0.52207562027796];
B = [0.04297742623024   0.09354433130786   0.09354433130786   0.04297742623024];
figure(1)
freqz(B,A)
figure(2)
zplane(B,A)