t=[0:0.02:1];
n=size(t,2);
R=100;
h=2*R/(n-1);
y=zeros(n,1);
y1=zeros(n,1);
x=zeros(n,1);
x1=zeros(n,1);
y2=zeros(n,1);
for i=1:n
  x(i)=-R+(i-1)*h;
  y(i)=0;
  y1(i)=R;
  x1(i)=R;
  y2(i)=(i-1)*h/2;
end;
plot(x,y,x,y1,x1,y2,-x1,y2,'k');