Time dependent shocks

Hi there.

I have a question about shocks in determinstic model. I am trying to impose a sequence of deterministic shocks that are function of time. Specifically, the shock looks like


where t is time and rho is a constant less than 1. Given enough time, the shock s eventually will reach zero.

Could any one show me how to impose it in the shock block?

Thanks a lot in advance.

You can basically follow

Thank you very much!

For f=0.9^t and t=1:10, You need something like