t=0:0.001:5;
f=8000;
fs=10000;
y=sin(2*pi*f/fs*t);
%plot(t,y);

error = zeros(1,20);

for n=1:20
    z=fi(y,1,(2*(n+1)),n);
    z1=z.data-y;
    error(n) = sum(z1.^2);
end

% z1=z.data-y;
% err=z1.^2;
n = 1 : 20;
stem(n,error)