code: def step(self, y, u, t, h):
  		
  		k1 = h * self.func(t, y, u)
  		k2 = h * self.func(t + .5*h, y + .5*h*k1, u)
  		k3 = h * self.func(t + .5*h, y + .5*h*k2, u)
  		k4 = h * self.func(t + h, y + h*k3, u)
  		return y + (k1 + 2*k2 + 2*k3 + k4) / 6.0
docs: This is called by solve, but can be called by the user who wants to
  		run through an integration with a control force.
  
  		y - state at t
  		u - control inputs at t
  		t - time
  		h - step size