How can i take double integral of a second derivative?

I am working on a problem in which I am taking the equations of motion of a quadcopter and applying PD control on them. As the result, I am getting the second derivatives of x,y and z. But I need the z value which is the displacement in z direction from the second derivative of z( its acceleration). I saw a simulink model where they took they placed the values through a integrator. Can I do something similar in my code?

Any help is appreciated.

Thanks.

[Sean de Wolski]

Are you using Simulink?

[luc]

This might be of help: integrating numeric data