function dudt = f_nodrag(t, u) 
% equations of motion for baseball in flight without air resistance
  
  g = 9.8;    % acceleration of gravity m/s^2

  % extract components of vector u into variables x, y, vx, vy
  x  = u(1);  
  y  = u(2);
  vx = u(3);
  vy = u(4);

  % compute rates of change of those components
  dxdt = vx;  
  dydt = vy;
  dvxdt = 0.0;
  dvydt = -g;

  % pack rates of change back into vector dudt, return value of function
  dudt = [dxdt; dydt; dvxdt; dvydt]; 
end