How to implement exponential smooting in powerpivot?

[sherifffruitfly]

Hi all, I'm having trouble getting an exponential smoothing measure going in powerpivot. This is where, a given time series {d_t} is transformed into the smoothed series {s_t} by means of convex combinations defined recursively: s_0 = d_0 s_t+1 = a * d_t + (1-a) * s_t It is immaterial to me where in the implementation the parameter 0 <= a <= 1 is set - magic constant or database-fed. I have a proper date dimension related to the time series table. Any tips on how I can implement this routine in powerpivot? many thanks, sff