Discrete systems using s-function

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dab483
dab483 2012-1-22
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.

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Kaustubha Govind
Kaustubha Govind 2012-1-23
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).
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Kaustubha Govind
Kaustubha Govind 2012-1-23
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;

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