function [y] = zerofilt(x,n,ip,a) 
      
y(1)=x(1);
if ip ~= 1
	for i=2:ip 
		y(i)=x(i);
		for j=1:i-1 
			y(i)=y(i)+a(j)*x(i-j);
		end
	end
end
for i=ip+1:n 
	y(i)=x(i);
	for j=1:ip 
		y(i)=y(i)+a(j)*x(i-j);
	end
end