clear;
x=[-20:0.1:20];
y=zeros(401,1);
for i=1:200
  y(i)=sin(x(i)/2)*2/x(i);
  y(i+201)=sin(x(i+201)/2)*2/x(i+201);
end;
y(201)=1;
plot(x,y,'black');
axis([-20 20 -0.5 1.5]);
axis on;