该程序可以用于验证DTFT的各种性质

				function y = circonv(x1,x2)
				L1 = length(x1); L2 = length(x2);
				if L1 ~= L2, error('Sequences of unequal lengths'), end
				y = zeros(1,L1);
				x2tr = [x2(1) x2(L2:-1:2)];
				for k = 1:L1
					sh = circshift(x2tr,1-k);
					h = x1.*sh;
					y(k) = sum(h);
				end