I'm trying to solve equation of a mass damper system shown in the image. The x (LHS) is the unknown displacement which is to be solved from the equation.I know y and dy/dx values at each instant of time (obtained from experiments). While solving using ode45 I'm not able to update the value of y and dy/dx for each time interval. How else can I solve the equation to get value of x. I used central difference scheme but the answer is diverging from the expected values drastically, when marched in time. Thank you in advance.