Simple Exponential Smoothing question

[StinkPalm]

Ok I built an exponential smoothing model in excel according to the equations:

S0=X0
St= αXt + (1-α)S(t-1)

Where S is predicted (or smoothed) value
X = observed value
α = alpha which is the smoothing factor between 0 < α < 1


Now according to my understanding of this equation if α = 0 then αXt part is 0 and thus the equation equals S(t-1). Furthermore S at time 0 is set to X at time 0 so that means the value is just held at X0.

But when I run the same model in SAS the result is not X at time 0 but instead it the value of my last observation of X not my first observation.

This is what is confusing me. Can any of you explain why there is a difference in results?

[quark]

I'd have a look at your SAS code. There seems to be an error in programming the equations.

[StinkPalm]

Instead in SAS if you go to the "Solutions" menu then the "Analysis" menu there is a selection for "Time Series Forecasting System". Once in there I select the model by clicking "Develop Model" and picking Simple Exponential Smoothing then I set the α=0 and run it.