function L=lpf(c0,c1,c2,c3,N)

for k=1:N/2 -1,
L=[L;zeros(1,2*(k-1)),c0,c1,c2,c3,zeros(1,N-(4+2*(k-1)))];
end

L=[L;c2,c3,zeros(1,N-4),c0,c1];
