## smth9

`smth9(expr)`

Performs a 9 point smoothing to the gridded result of the `expr`.

### Usage Notes

1. The result at each grid point is a weighted average of the grid point plus the 8 surrounding points. The center point receives a wieght of 1.0, the points at each side and above and below receive a weight of 0.5, and corner points receive a weight of 0.3.

2. All 9 points are multiplied by their weights and summed, then divided by the total weight to obtain the smoothed value. Any missing data points are not included in the sum; points beyond the grid boundary are considered to be missing. Thus the final result may be the result of an averaging with less than 9 points.

3. If the gridded data is 1-Dimensional, the result is a 3 point smoothing.

### Examples