n = 10000;
m = 201
astart = 2;
aend   = 4;
x = .2;
for k=1:n
   a = astart + (aend - astart)*k/n;
   for i = 1:m
      x = a*x*(1-x);
   end
   aplot(k) = a;
   xplot(k) = x;
end
plot(aplot,xplot,'.')
title('A picture of the Feigenbaum cascade')