Discrete systems using s-function

Hi,

i have this discrete function, and try to simulate it using s-function level 2, where k represent simulation length from 1 to 50sec.

x(k) = 0.5*x(k-1) + 25*x(k-1) /(1 + x(k-1)^2) + 8 cos(1.2(k-1))

here how i put it in the s-function level 2:

function Update(block)
Q=1;

xplus = 0.5 * xminus + 25 * xminus / (1 + xminus^2) + 8 *     cos(1.2*(k-1)) 

block.Dwork(1).Data = xplus;

where xplus = x(k) xminus=x(k-1)

but i am not sure about cos(1.2*(k-1)). Can anyone pls advise how should i implement this? Thanks.

Answer 1

[Kaustubha Govind]

Is (k-1) basically "t" at the previous step, where t is the current simulation time-step? If yes, you can store "t" in a Dwork by using block.CurrentTime and use it in the next time step as (k-1).

[dab483]

how to store t in Dwork using block.CurrentTime. Never use this before.

[Kaustubha Govind]

Same way you are storing 'xplus' in your example:

% Register two DWorks in DoPostPropSetup

block.NumDworks = 2;

% In Update

block.Dwork(2).Data = block.CurrentTime;

[dab483]

Thank you very much..