function yp = matlorenz(t,y)
  
  % the coordinate axis [x;y;z] = [y(1);y(2);y(3)]
  sigma = 10;
  b = 8/3;
  r = 24.5;
  yp = [sigma*(y(2)-y(1));r*y(1)-y(2)-y(1)*y(3);y(1)*y(2)-b*y(3)];


