SMTH9 Function

[Stephen R McMillan]

The GrADS documentation provides the method for the 9-point smoothing in 
the SMTH9 function. However, for 1-D data, it only says "If the gridded 
data is 1-Dimensional, the result is a 3 point smoothing." Can any user 
tell me what the specific method is? It does not appear to be a straight 
3-point average, but some weighted average. I've tried various 
combinations but haven't been able to duplicate the GrADS result.

I'm using SMTH9 within a GR2STN expression in a 2-D (lon-lat) field; x, y, 
and t are fixed for each time step. Sample script expression:

'd gr2stn(1.8*smth9('var')-459.69,'lon','lat')'

I get a different result if I first re-define the variable as a smoothed 
field (using smth9), and then run the expression without smth9. In this 
case, the result equals the 9-point smoothing I would expect. Why the 
difference?

I'm using version 1.9.0-rc1 (from OpenGrADS) for Windows, run on a Windows 
XP platform.

Stephen McMillan


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