int v to x const a

• Velocity $$\tag{B1} v(t) = v_n + a(t - t_n), \ \ \ \ t_n \le t \le t_{n+1}. $$
• Initial condition $$\tag{B2} x(t_n) = x_n. $$
• Posisition $$\tag{B3} x(t) = x_n + v_n(t - t_n) + \tfrac12 a_n(t - t_n)^2, \ \ \ \ t_n \le t \le t_{n+1}. $$