for i=1:91,
   for j=1:81,
      y(j) = (j-1)/40 - 0.5;
      x(i) = (i-1)/30 - 1.5;
      z(j,i) = 100*(x(i)*x(i)- y(j)).*(x(i)*x(i)- y(j)) ...
         + (1 - x(i))*(1 - x(i));
   end;
end;
contour(x,y,z,[1 2 3 4 5 8 12 16 20 30 50 80 120 200])
grid on;