%% Design Lowpass SOS Filter
% By default, fdesign and design functions return SOS filters when possible. This example designs a lowpass SOS filter that uses fixed-point arithmetic.

d = fdesign.lowpass('n,fp,ap,ast',40,0.55,0.1,60);
hd = design(d,'ellip','SystemObject',true);

% Using the issos function, verify whether the designed filter is in SOS form.

IsSOS = issos(hd)

% The filter is in second-order section form.
%
% Copyright 2012 The MathWorks, Inc.